The Philosophy of Gutloading
I would like to thank Anthony Herrel and Walter Tapondjou for their helpful advice on where to look for relevant papers.
Recently, it was suggested to me that our current gutloading practices might be wrong-headed. In particular, I was told that because chameleons cannot digest much of the plant material we are feeding our bugs, that they derive no benefit from our sometimes-monumental gutloading efforts. This struck me as odd, since I thought the point of gutloading was to have the bugs do the digesting—thus turning what would be indigestible plant matter into nutrients that our chameleons can access. Maybe, however, my interlocutor was right in calling this a fairy tale. Maybe, it isn’t healthy to have such a multitude of ingredients in our gutloading regimes—ingredients that are not only foreign to chameleons, but which might not even contribute to chameleon nutrition because they cannot be digested.
In all fairness, I think the point s/he was trying to make was that wild chameleons rarely eat large nutrient-dense food items, consuming instead many small nutrient-poor insects such as flies, bees and beetles. There is certainly evidence to support this. Several researchers have noted a high percentage of dipterans (flies) in the diet of multiple species (Tapondjou, 2019), (Karen-Rotem, Bouskila, & Geffen, 2006). Tapondjou’s study focuses on the montane species of Cameroon (e.g. T. montium, T. quadricornis, etc.), while Karen-Rotem et al. observe fruit fly predation on the Seychelles. Likewise Pleguezuelos et al. report that during the spring, the diet of Chamaeleo chamaeleon is comprised heavily of hymenopterans—i.e. bees and wasps (Pleguezuelos, Poveda, Monterrubio, & Ontiveros, 1999). Finally, Burrage notes a significant level of coleopterans—ground beetles, in particular—in the diet of some chameleons (Burrage, 1973).
This blog is intended to explore the philosophy of gutloading. In particular, I want to investigate whether the view suggested to me in my conversation (see paragraph 1), presents good reasons for changing our gutloading regimes. While I will certainly be relying on as much empirical research as possible, I also want to add some conceptual analysis to the debate, so please forgive my penchant for the armchair. Finally, I want to make clear that my attempting to address the content of certain online information is precisely that—an attempt to address the content. If information is proffered as empirically based, it is subject to scrutiny on that very same empirical basis. If arguments are martialed on a conceptual basis, they too are candidates for conceptual evaluation. Nowhere in what follows will I be engaging in ad hominem attacks, and I sincerely hope that my work here will not be perceived as such.To work, then…
2. Categorizing the views
Some organizational housekeeping is in order at the outset. I want to define two broad camps with respect to gutloading:
• Theory 1: We gutload to increase the nutrient content of our feeder insects. Our access to feeder variety comes nowhere near the wild diet, which we assume is replete with a variety of nutrients derived not only from the diversity of the wild insects consumed, but the variety in their respective diets. We infer from the fact that chameleons appear to have demanding nutritional requirements, and from the fact that our feeder insects fall far short of said requirements, that the wild insects on which our chameleons prey must be chalk-full of essential nutrients. If not, how are wild chameleons having their nutritional needs met? Our intuitive response is to feed our feeder insects a variety of nutrient rich foods in the hopes of compensating. Such items include common plant-based fare such as apples, oranges, bananas, blueberries, carrots, squash and various high calcium greens. Other additives include bee pollen, spirulina powder, hibiscus flowers, prickly pears, nuts, kelp, and powdered plant products such as mulberry, hibiscus and alfalfa powders.
• Theory 2: Some of the most common insect prey of many wild chameleons are small items such as flies, bees, wasps and beetles. Among other things, these insects are often involved in pollination, and will certainly be carrying pollen and nectar both on them, and in their gut contents. Chameleons must therefore consume large amounts of pollen and nectar. The consumption of these small insects, coupled with their pollen/nectar content, satisfies the majority of the nutritional requirements of our chameleons. Obviously, there will be other less commonly consumed insects (and even vertebrates), but bees, wasps, flies, beetles and their pollen/nectar content account for a majority of chameleon nutrition.
Unfortunately, as stated, these two theories are not inconsistent. For instance, if it turns out that e.g. a bee and its pollen content contain roughly the same nutrients as some complicated concoction of collard greens, spirulina, oranges and hibiscus powder when fed to some variety of roach, then the two views end up agreeing about what nutrients we ought to be giving to our chameleons via gutloading. They just disagree about how we ought to deliver those nutrients. One side says by feeding bees (wasps, flies etc.) sufficiently gutloaded with, and coated in, pollen; the other side says by feeding commonly available feeder insects a complicated concoction of the ingredients listed in theory 1. Some further item/s of contention must stand in between the relevant parties. I shall hazard a few guesses:
a. In fact, the most common food items consumed by wild chameleons are actually nutritionally poor. Chameleons are perfectly adapted to live on such a diet.
b. This obsession with packing so many foreign nutrients into our feeders might actually be causing shortened life expectancy due to toxic effects, or obesity.
c. Relatedly, no one has ever studied the nutritional make-up of the wild chameleon diet, so there just isn’t any evidence to support the fact that the gut contents of an insect that has eaten e.g. butternut squash are at all helpful.
d. What we ought to be aiming for is to replicate those aspects of the chameleon diet that chameleons have evolved (over thousands of years) to experience.
e. Chameleons cannot digest most of the items theory 1) would have us feed to our insects, such as blueberries, kale or spirulina. So, as it turns out, our efforts here are futile.
There are doubtless more implicit premises here, and theory 2) is not restricted to only one. What is important is that some combination of additional corollaries must to be at work, if the disagreement is substantive.
I propose to deal with the conceptual points first, so that the proceeding parts of the blog can deal with the empirical evidence. The conceptual points, so far as I can see, are c and d. Premise c. makes the claim that no one has ever studied the nutritional make-up of the wild chameleon diet. While that is an empirical claim, the inference that there is thus no evidence to support the use of ingredients such as butternut squash in our gutloads has a conceptual implication. Namely, if it is true that that no one has ever studied the nutritional make-up of the wild chameleon diet, then there is also no evidence to tell against the use of butternut squash in our gutloads. A lack of any empirical data cannot be used to tell against one option while simultaneously supporting the other. The absence of data seems like a pretty poor evidentiary candidate for either side. Moreover, if it is true that no one has every studied the nutritional make-up of the wild chameleon diet, then the first claim in a. seems puzzling. How do we know the gut contents of dipterans and hymenopterans are nutritionally poor, given that no one has studied this (as per c.)? To be fair, it doesn’t make a lot of sense for flying insects to be bursting with gut contents—they have to fly after all.
Premise d. makes a normative claim about how we ought to approach chameleon husbandry. While I have no problem with some normative claims in this context, this particular one is tenuous. Humans have evolved teeth to last them throughout their natural lives (when our average lifespan was 25-30). Unfortunately, we now live far longer than our teeth can last without assistance. Sometime in last few hundred years we noticed that regular brushing of our teeth contributed to their longevity. Indeed, a more recent development showed that the use of fluoride in toothpaste helped even more. Both of these tooth husbandry practices can be thought of as unnatural. However, since living to 85 is unnatural, and we want to live to 85, we have to employ unnatural husbandry techniques to see that we are able to eat chicken wings well into our 60’s. More to the point, it seems like chameleons are living longer in captivity than they ever do in the wild. So, while the nutritional requirements they have evolved to live with in the wild might be sufficient for a 2 year lifespan, what about a 10 year lifespan? In short, it is not entirely obvious that we ought to tailor our nutrition regimes to match nature, since captives are already living unnaturally long lives.
3. The wild chameleon diet.
I cited some data in the second introductory paragraph that suggests that dipterans, hymenopterans and coleopterans constitute a large part of the diet some wild chameleons (Burrage, 1973) (Karen-Rotem, Bouskila, & Geffen, 2006) (Necas, 2019) (Pleguezuelos, Poveda, Monterrubio, & Ontiveros, 1999) (Tapondjou, 2019). This was partly in the service of making theory 2) appear less incredible to those who have never encountered it. What I did not mention was that wild chameleons also consume a large number of other insects. Moreover, the percentage any one order of insects in the diet of wild chameleons varies strongly with the time of year. Insect populations wax and wane with the season, as do the feeding grounds of many chameleon species. Caterpillars, abundant in the spring, disappear in the summer to be replaced by their adult form. Carrion flies abound during periods of drought and famine when large numbers of animals fall victim to starvation/dehydration. Even the abundance of bees has a natural ebb and flow. This is merely to point out that chameleons are indiscriminate feeders, consuming prey items according to their abundance (Necas, 1999/2004, p. 34). It is therefore unsurprising to find that although dipterans and hymenopterans figure heavily in the spring diet of C. chamaeleon—29% and 32%, respectively—orthopterans (which include crickets and locusts) comprise 40%-50% of the diet in summer and fall (Pleguezuelos, Poveda, Monterrubio, & Ontiveros, 1999).
After flushing the stomach contents of several species, Tapondjou (2019) reports four orders of arthropods as comprising the lion’s share of the trioceros species of Cameroon. In order from highest frequency to lowest these are as follows: dipterans (flies) and coleopterans (beetles), with hemipterans (plant sucking true bugs, e.g. cicadas, aphids, etc.) and orthopterans (crickets and locusts) tied for the number three spot. Surprisingly, a 2003 study of Trioceros montium, T. pfefferi and T. quadricornis reveals some additional high percentage food items including arachnids (spiders), lepidopterons (moths/butterflies), and blattodeans (cockroaches, termites, mantids) (Hofer, Baur, & Bersier, 2003). The findings below have been reproduced from (Hofer, Baur, & Bersier, 2003):
There is no doubt that dipterans and hymenopterans play a significant role in the wild diet. However, these numbers also suggest that spiders (arachnids), crickets/locusts (orthopterans), true bugs (hemipterans/heteropterans), butterflies/moths/caterpillars (lepidopterons), beetles (coleopterans), and cockroaches/termites (blattodeans) play a significant role. Indeed, arachnids and heteropterans appear to rank ahead of both dipterans and hymenopterans in the diet of T. montium, and continue to rank among the top food items for all three species. Again, this does not tell against the importance of flies and bees in the wild diet, but it certainly suggests a variety in the wild diet of these three species.
In a similar study of Rhampholeon spectrum, Trioceros owenii, T. cristatus and Chamaeleo gracilis, Akani et al. reveal that orthopterans rank among the top food items consumed. The findings of Akani et al. are reproduced below (Akani, Ogbalu, & Luiselli, 2001):
Surprisingly, dipterans are poorly represented in this data. And, with the exception of the abundance of ants and termites found in the ground dwelling species (R. spectrum and T. cristatus), the next runners up after orthopterans are arachnids, lepidopterons, and hemipterans. Note that vespoidea, apoideae (both in hymenoptera) and coleopterans figure minimally in the diet of all four species. While this might be surprising, there is still plenty of evidence for the relative frequency of dipterans and hymenopterans in the diet of wild chameleons. In a study about the relationship between bite force and prey hardness, Measey et al. provide the following data (Measy, Rebelo, Herrel, Vanhooydonck, & Tolley, 2011):
This study shows the high percentage of hymenopterans, dipterans and coleopterans in the wild diet of Bradypodion pumilum. But once again, hemipterans, lepidopterons, arachnids, and (to a lesser extent) orthopterans, figure importantly in the results. Now, it should be noted that B. pumilum is a diminutive species, so the abundance of collembolans and absence of larger prey items is not surprising.
In a similar study, the diets of Bradypodion melanocephalum and B. thamnobates are assessed (Da Silva, Carne, Measey, Herrel, & Tolley, 2016). Here too, dipterans are well represent—as are coleopterans, arachnids, and orthopterans. Hemipterans constitute a huge portion of the diet of B. melanocephalum, and isopods appear to be the prey of choice for females of the species. Curiously, hymenopterans rate low relative to the dipterans. It is important to note that in this and the previous study, wild diets vary with the biotopes of the relevant species: the grassland populations consume different proportions of various prey items than those from the forest. While not surprising, this last fact supports the opportunistic aspect of the wild diet: chameleons eat what they can get. Trivial though such a fact seems, it might have more explanatory force than it appears to. I’ll come back to this in the foot notes, but just consider which insects are likely to occupy the most geographical range when mobility is concerned…Anyways, back to the last chart; reproduced here are the findings of Da Silva et al. (Da Silva, Carne, Measey, Herrel, & Tolley, 2016):
So what does all this have to do with gutloading…remember gutloading? This blog is about it. Well, recall that the view levied against our common gut-loading practices insists that the wild diet of chameleons consists mainly of dipterans, hymenopterans and coleopterans; i.e. flies, bees and beetles. And an accompanying thesis was that the only nutrients we know for sure that these insects contain are those contained in the pollen with which they are in frequent contact. That is, our focus with respect to gutloading should be on pollen and its ilk. While it certainly appears that chameleons ingest a lot of pollen given their proclivity for dipterans, what about the other prey items that are often consumed in relatively high numbers? What of the orthopterans, hemipterans, isopods, arachnids, lepidopterons and blattodeans? Indeed, even the beetles—touted as important in virtue of their pollen content—are a diverse group, many of which are detrivorous and folivorous. A good percentage of so-called “true-bugs”, i.e. hemipterans, are sap-sucking folivores—extracting nutrients from the sap of a wide variety of plants. And I imagine that the gut contents of spiders would count as bioavailable par excellence, since their venom liquefies the nutrients of their prey. It seems like these other arthropods might contribute to the overall nutrition of wild chameleons, since they in fact appear to represent a significant portion of the wild diet.
To summarize, chameleons do in fact consume many dipterans, coleopterans and some hymenopterans. However a study shows that T. montium, T. pfefferi and T. quadricornis consume more hemipterans than hymenopterans, and more arachnids than both. Orthopterans, Lepidopterons, coleopterans and blattodeans also occupy significant portions of one or more of their respective diets (Hofer, Baur, & Bersier, 2003). Surprisingly, another study reveals that dipterans figure low in the diet of R. spectrum, T. owenii, T. cristatus and C. gracilis—all of which appear to rely heavily on orthopterans, arachnids and, to a lesser extent, lepidopterons (Akani, Ogbalu, & Luiselli, 2001). Interestingly, T. cristatus appears to have a penchant for dragon/damselflies. This last point is interesting since, so far as I know, the order Odonata is composed exclusively of carnivores, so there isn’t a lot of pollen gathering there. Just as interesting, the larval phase of many dragon/damsel flies is aquatic, which means some chameleon food chains have aquatic origins. Our Bradypodion species certainly consume many dipterans, but hemipterans figure just as importantly in the data. Dipterans take the number one spot in the wild diet of B. pumilum, but hemipteran and coleopteran numbers are double those of hymenopterans (Measy, Rebelo, Herrel, Vanhooydonck, & Tolley, 2011). Hymenopterans figure equally poorly in the diet of B. melanocephalum and B. thamnobates, which prefers dipterans, hemipterans, arachnids, coleopterans and orthopterans (Da Silva, Carne, Measey, Herrel, & Tolley, 2016).
While all this data is interesting, it is far from conclusive. Dietary data from 5 studies covering only 10 species is far from the whole picture. Worse still, the studies focus on less commonly kept species, instead of veileds, panthers and Jackson’s, so it is not clear how relevant the data is for us. However, information is scarce here, and we can only do what we can with what we have. What we can glean is this: some chameleon species consume large amounts of non-pollinating insects as well as pollinators. And while chameleons have been observed positioning themselves on bushes frequented by bees and other pollinators, the above data seems equally important. That being said, we have not yet investigated the nutrient contents of pollen; so it could turn out that, regardless of what the abovementioned insects bring to the nutrient table, so to speak, pollen will already have it.
Bee pollen is used the world over for its many reported health benefits; and just as it is used all over the world, so too is it farmed. There appears to be scarcely a continent on which bee pollen isn’t harvested for commercial use. Unsurprisingly, the nutrient content of pollen collected from various locations differs. (Gardana, Del Bo, Quicazan, Correa, & Simonetti, 2018). However, a general picture seems possible. Reproduced below are three charts—1. (Denisow & Denisow-Pietrzyk, 2016), 2. and 3. (Human & Nicolson, 2006)—representing some of the main nutrients in pollen. Again, nutritional data varies from region to region, but charts 2. and 3. are from the pollen of a plant native to southern Africa:
1. 2. 3.
As I just spent several pages displaying a variety of charts, I will confine myself to a summary here. Bee pollen contains a multitude of nutritrients including proteins, carbohydrates, lipids, vitamins and minerals. The information on the chemical composition of bee pollen is widely available, and the reader can look at as many graphs and charts as s/he wishes. More importantly, the benefits of bee pollen in a gutload regime are not in question. What is in question is whether bee pollen would suffice as the primary gutload ingredient.
While interesting, data from several studies suggests that pollen might be lacking certain elements that we have come to believe are important for chameleons (though admittedly, this assumes we actually have a clue about chameleon nutrition). In a previous blog entry, the role of carotenoids as possible substitutes for preformed vitamin A was examined in detail. The stumbling block there was that, on one reasonable interpretation of the data found in Dierenfeld et al. (2002), chameleons appear not to be able to convert beta-carotene and beta-cryptoxanthin into preformed vitamin A. While the data is not conclusive, it has been suggested that perhaps some other carotenoid could fill this important role. The problem is that several studies show bee pollen to contain no more than five of the over one thousand known carotenoids (Margaoan, et al., 2014), (Gardana, Del Bo, Quicazan, Correa, & Simonetti, 2018), (Qiang-Qiang, Wang, Marcucci, Sawaya, Xue, & Wu, 2018), (Denisow & Denisow-Pietrzyk, 2016), (Margaoan, et al., 2014). Two of these, beta-carotene and beta-cryptoxanthin, are the carotenoids mentioned in the Dierenfeld study; another, lutein, is not a vitamin A precursor. For clarity’s sake, if a wide assortment of carotenoids is an important part of chameleon nutrition, then it seems like we’ll have to use some high carotenoid ingredient in our gutloads, in addition to bee pollen.
Another shortcoming of bee pollen is that it appears to have a poor calcium to phosphorus ratio. In Qiang-Qiang et al. (2018), pollen samples contained .2-5.8mg of calcium/100g of dry pollen, and .8-9.6mg of phosphorus/100g of dry pollen. Similar data appears on the above chart from Denisow et al. (2016). Again, this is not a strike against pollen per se, but merely data that suggests that wild chameleons must be getting enough calcium to not only offset the poor ca : p ratio of insects, but also of the large amount of pollen they are said to consume. Indeed, one might surmise that chameleons either have a steady environmental supply of calcium (dust on the leaves?), or else, that they’re finding prey that contains sufficient levels to buffer the poor ca : p ratio found in the high numbers of pollinators they are said to eat…or both.
To sum up, all sides agree that pollen is an excellent addition to any gutloading regime. However, it is entirely plausible that a vast assortment of carotenoids—carotenoids that pollen appears not to have—might be an important factor in chameleon nutrition (see my blog entitled The Current StAte, and Dierenfeld, Norkus, Carroll, & Ferguson, 2002).Pollen also appears to have a poor calcium to phosphorus ratio (Qiang-Qiang, Wang, Marcucci, Sawaya, Xue, & Wu, 2018), which means additional calcium is required. There is certainly more work to be done here. I want to mention one final slightly problematic attribute of pollen—namely, the fact that its digestibility has recently come into question (Franchi, Franchi, Corti, & Pompella, 1997). The aforementioned study focuses on human digestion, but one wonders whether chameleons would fare any better. Since chameleons have short digestive tracts incapable of processing hard to digest material such as plant matter (Necas, 2018a), one wonders whether pollen would present a challenge. On the other hand, this might be a moot point, if the pollen-bearing insects have already done some of the digestive labour for the would-be chameleon consumer…
5. Insects and the work they do
As I said previously, I was under the impression that though chameleons can’t digest many of the gutload ingredients we use, they can certainly access the nutrients of these ingredients via the gut contents of our feeder insects. In other words, chameleons do not have to digest the gutload ingredients because the insects have already done the heavy lifting—reducing relatively indigestible (for chameleons) ingredients to bio-available nutrients. It was thus surprising to learn that, whether overtly, or by implication, some researchers found this view dubious. While I do not have the skills required to do justice to the biochemistry of insect digestion, I can perhaps say a few intelligent things. For a sad gloss of insect digestion, see the endnotes .
A recent study suggests that—in addition to the help from the symbiotic microorganisms found in the digestive tracts of many insects—insects themselves are capable of breaking down a notoriously difficult to digest substance—namely, cellulose (Calderon-Cortes, Quesada, Wantanabe, Cano-Camacho, & Oyama, 2012). That insects have developed means of doing this is evidence of a robust digestive system. More to the point, several studies show that insects have the ability to reduce many otherwise indigestible food items to bio-available nutrients for the animals that consume them. Evidence from Feltwell (1974)and Carroll et al. (1997)supports that plant-eating insects—lepidopteron larva, in this instance—sequester a variety of carotenoids from their herbivorous fare; and one study traces the flow of these nutrients to the plumage of the insectivorous birds that eat them (Partali, Liaaen-Jensen, Slagsvold, & Lifjeld, 1987). This last study is significant because the intermediate lepidopterons not only broke down the relatively difficult to digest leaves containing the carotenoids, but the study also found that the carotenoids were passed on to the birds unchanged; i.e. the caterpillars broke down the plant matter into nutrients that they themselves did not assimilate, but passed straight on to the birds in a usable form—presumably via their gut contents.
I belabour this point not because I find it particularly ground breaking (it’s basically just an example showing that food chains exist), but because this appears to be in doubt by advocates of theory 2). When a chameleon’s inability to digest certain gutload ingredients is used as an argument against theory 1) this is precisely what is being argued. More clearly, to argue that we should not use e.g. squash in our gutloads because chameleons can’t digest it, just is to deny/ignore the digestive work of the intermediate insects. As a side point, I have heard arguments to the effect that e.g. blueberries should not be used in our gutloads because blueberries are very unnatural to chameleons. If our gutload ingredients are broken down to their constituent nutrients by our insects, then it does not seem to matter whether these nutrients are derived from blueberries, or the native flora of Madagascar. Perhaps, however, I misunderstand. Perhaps the point is that it is doubtful that the insects can digest many of our gutload ingredients. While I don’t think this is the case, there is evidence that even synthetic material is not immune to the digestive efficiency of some insects. In a recent study, mealworms were able to survive on, and digest, Styrofoam (Nukmal, Umar, Amanda, & Kanedi, 2018). While I would advise against gutloading with this particular ingredient, this suggests that insects really are prodigious digesters.
6. Flamingoes and Fish and Flies, oh my!
Between 10 and 25 million years ago, the surface of the earth expanded with the divergence of two plates in what is today east Africa. Spanning from the southern part of Sudan, and stretching south as far as Mozambique , this great rift valley, as it has become known, is a hot spot for chameleon diversity—second only to Madagascar in both diversity and endemism (Tolley & Herrel, 2014).
A multitude of other species also calls this oasis home. Among them is the lesser Flamingo Phoeniconaias minor Geoffroy—a species that seasonally inhabits both the three giant rift lakes—known for their endemic populations of the cichlids so beloved in the tropical fish hobby—and the high altitude lakes on either side of the eastern rift. Recently both the flamingo and some cichlids species have come under the threat of pollution. In particular, heavy metals have begun poisoning the main food source they share (Ballot, et al., 2004), (Vareschi & Jacobs, 1985). Not confined to the larger, low altitude rift lakes of Malawi (500m a.s.l.) and Tanganyika (773m a.s.l), the contamination has lead to several mass die-offs in the high-altitude lakes of Bogoria (990m a.s.l.), Victoria (1135m a.s.l.), Elementeita (1670m a.s.l.) and Nakuru (1760m a.s.l.) (Ballot, et al., 2004). The cichlid and flamingo populations are not the only victim of the environmental pollution: chironomid larva are also significant consumers of the contaminated resource (Vareschi & Jacobs, 1985).
Since chironomids are dipterans, and since we know dipterans figure centrally the diet of many wild chameleons (see above), it seems like any chameleons in the affected areas might be at risk. Since this area is home to many species of Trioceros, Kinyongia and Rieppellion—especially those that prefer higher elevations—it appears even the wild brethren of our beloved pets are not immune. Though concerning, this is not news. That pollution affects wild animals the world over is hardly an earth-shattering revelation. Indeed, some of the referenced studies are decades old, and wild chameleons are far more threatened by habitat loss than they are this particular problem.
So what exactly is the point here? This blog is about gutloading, right? Fair enough…If you think that the pollutants in the food source could be passed on to chameleons because they eat the flies whose larva eat the food source, then you should also believe that the nutrients in the food source could also be passed on to the chameleons. Interestingly, one of the gutload ingredients that has figured prominently in recent gutloading debates is this very food source that holds such a place of importance in some of the food chains in the rift valley: Arthrospira platensis, i.e. one of the main sources of the dietary supplement we know as spirulina. In a rare moment of literary coincidence, one of the gutload supplements that has caused such a rift in the philosophy of gutloading occurs centrally in the Great Rift Valley, whence comes many of our favourite species.
The arguments proffered against the use of spirulina generally come in one of two forms. The first is to question whether chameleons can even digest spirulina. We looked at this in the section on insects. There was evidence to show that insects are excellent at breaking down hard to digest elements into nutrients that are bio-available to the animals that consume them. And while we didn’t look at spirulina directly, we know that the larva of some dipterans feed on in. So, all in all, there appears to be good reasons to think that it doesn’t matter whether chameleons can digest it, since the insects that we feed them can.
The second kind of argument against spirulina contends that spirulina is pretty foreign to the wild chameleon diet, and wild chameleons would almost never encounter it within their food chains. We have just seen evidence that not only does spirulina occur in the wild ranges of many species (even at high elevations), but it figures importantly in several food chains. Yes, it is an aquatic algae (actually it’s a cyanobacteria, but no matter), but we know food chains can cross the aquatic/terrestrial threshold. Dragonflies are one example (remember T. cristatus appears to love them); but more importantly, there are other species of dipteran whose larva actually live off the relevant algae (see Vareschi & Jacobs, 1985). We know from the wild diet studies we examined, dipterans are some of the most common prey items of many species. And while this is far from definitive proof, I find it perfectly plausible to think that spirulina is not all that foreign to wild chameleons. Indeed, I would be surprised if there weren’t more than just one or two species of larval dipterans that consumed spirulina (Arthrospira platensis), and that the nutrients therefrom reach the wild chameleon species of the area with sufficient frequency to make a nutritional difference/contribution. One final relevant fact about spirulina is that it’s not confined to mainland Africa. The freshwater and brackish lakes of Madagascar are also home to abundant populations of the relevant species (Scheldeman, et al., 1999). Below, I have reproduced a distribution map that focuses on just one species of chameleon whose natural range coincides with some of the lakes mentioned above. The map is courtesy of Bill Strand and Petr Necas (Strand & Necas, 2018).
7. Tallying up the data…and maybe some more conceptual analysis
So where exactly are we with respect to the gutloading debate? This has been a long and arduous trek through conceptual analysis, the wild diet of ten species of chameleons, insects and their amazing digestive power, food chains, the nutritional value of bee pollen, and the distribution of the cyanobacterial sources of spirulina. But what have we actually accomplished?
We began with two approaches to gutloading. I’ll reproduce both theories below.
1. Chameleons have demanding nutritional requirements, which we assume are met by the variety of insects they eat, and the variety of nutrients those insects contain.
2. We can’t replicate this variety in captivity so...
3. We gutload to increase the nutritional contents of our feeder insects in the hopes of making up for this deficiency.
4. Ingredients include apples, oranges, bananas, blueberries, carrots, squash and various high calcium greens. Other additives include bee pollen, spirulina powder, hibiscus flowers, prickly pears, nuts, kelp, and powdered plant products such as mulberry, hibiscus and alfalfa powders.
a. Flies, bees and wasps are the main food items in the wild chameleon diet.
b. These food items are not stuffed full of plant material, they generally contain pollen.
c. Pollen is one of the few good gutloading ingredients, and when combined with the nutritional value of the insects bearing the pollen (bees, wasps, etc…) the combination ought to satisfy the bulk of a chameleon’s nutritional requirements.
d. Since chameleons can’t digest plant material, stuffing our insects full of plant material is pointless (and may even be harmful?).
What I wanted to know was whether theory 2) offered good reasons to rethink the gutloading practices in theory 1). I began to investigate the empirical strength of each point. In section 3, we looked at the admittedly scant data available on the wild chameleon diet. The studies suggest that while dipterans, hymenopterans and coleopterans do play an important part in the wild diet, hemipterans, orthopterans, and arachnids and often lepidopterons, play an equal role. Indeed, in several of the studies, orthopterans and hemipterans and even arachnids were just as common as dipterans in the wild diet, and much more so than hymenopterans. This suggests that whatever nutritional elements these other insects bring to the table might be important to take into account when deciding on our gutloading regimes. So, in contrast to the first point of theory 2), there is evidence that suggests that flies, bees and beetles do not occupy the overwhelming majority of the wild chameleon diet. However, because we didn’t yet know whether pollen could account for the majority of the nutrients found in the other commonly consumed insects, we looked briefly at the nutritional value of pollen (section 4).