Friday, March 8, 2019

My Opinion: Trilobite Beetles (Platerodrilus spp.) In Captivity

Trilobite beetles, Platerodrilus spp., (once known as Duliticola), are some of the most well known and popular insects in the world, even many "normal" people who can't tell the difference between a cockroach and a longhorn beetle know about these little gems of the natural world, and are usually stunned by the unusual body shapes and often beautiful coloration of the larvae and adult females. Some people obviously think these beauties highly resemble the extinct but famous trilobites, thus the common name for this genus, (I for one don't think they resemble them more than isopods do, why aren't isopods called "mini trilobites" again?).

Platerodrilus ruficollis. Image courtesy of Nicky Bay
















Of course, if they are as popular as they are with the insect fearing masses, you can guess that they are obviously one of the most wanted insects in any invertebrate breeder's collection! A couple Asian vendors have been selling some Platerodrilus as of late, and some European breeders will make trips to their native habitats and collect them for themselves, so I've been seeing a lot of posts about these beetles pop up in various breeder groups online, often accompanied by many, many comments from other people who want some trilobite beetles themselves.

However, most people who know anything about Platerodrilus know that they are notoriously poor captives; no one has ever bred them successfully, (though in one instance three larvae were hatched from eggs collected in the wild, but they died within weeks) and most imported larvae die before maturing. However when it comes to why that is, most people don't know the answer, so I figured I'd write up this post to help inform people as to why these beetles are not good captives, and likely never will be.

Platerodrilus sp. Image courtesy of Nicky Bay

















Issue #1) Diet:

Surprisingly enough, even the world's leading experts on these beetles are not 100% sure what they feed on, and up until relatively recently, there was some conflict as to what their diet consisted of. However, the most popular and widely accepted theory is that these beetles feed on microorganisms living within the juices of rotten logs, as outlined in the findings of Alvin T. C. Wong (1996). Most Platerodrilus experts agree with Wong on that, so for now it should be treated as fact.

Now it's likely true that most of the microorganisms they feed on in the wild are likely endemic to their native habitats, and if that's the case then it's probable that microorganisms found in rotten logs from Europe and North America just wouldn't be enough to sustain Platerodrilus. Additionally, it's also unlikely that most of the microorganisms that Platerodrilus feed on could proliferate in a hobbyist's enclosure, especially if switched to a different wood type. Also, who knows what specific combination of microorganisms are needed for them to survive?

Now, one could theoretically feed trilobite beetles by giving them unsterlized rotten logs from their native habitat, however that is an unfeasible plan for any hobbyist that lives outside of their native habitat, and would be very unsustainable at that, taking away food and living quarters for wild trilobite beetles. Additionally since the logs couldn't be sterilized, there's no telling what pests could be dwelling within them, and they might thrive in your Platerodrilus enclosure more than the trilobite beetles themselves, and harm them in the process!

Seeing as their only known food source would be extremely difficult or impossible to cultivate in captivity, and likely very unethical to import, it's not likely that any hobbyist will ever be able to adequately feed their Platerodrilus in captivity. Case in point, most breeders' trilobite beetles die mere months after getting them, likely from starvation. They often seem to be doing well for a few months, but in reality they are likely just slowly starving. They don't seem to have a fast metabolism, and can likely go months without an adequate diet, (which isn't uncommon for beetle larvae). Any that molt in captivity likely just had enough food reserves left in them to molt once, and will probably die shortly after.

EDIT: It's been brought to my attention that there are photos of Platerodrilus spp. feeding on slime mold, so microorganisms within rotten log juices are not the only documented food source for these beetles. However, it's unclear whether or not Platerodrilus spp. need specific species of slime molds to feed on, whether they need a combination of slime molds and rotten log juices or not, or whether slime molds are even needed in their diet, they could just be an unnecessary supplement to their main diet. Thus, this finding doesn't really change much. More scientific observations of wild individuals are needed to find out what is neccesary in their diet before being kept by the average hobbyist.

Platerodrilus ngi. Image courtesy of Nicky Bay

















Issue #2) Breeding:

Now, as many people know, adult female Platerodrilus look exactly like large, slightly more developed larvae, something known as neoteny. However, unbeknownst to many people, adult male Platerodrilus are actually winged, and look like your typical Lycidae adult... Oh yeah, and they are TINY, usually less than a quarter of the size adult females are. So you can pretty much be sure that ANY trilobite beetle larvae you ever buy are not male larvae, as only medium to large larvae (and maybe adult females) are collected and sold, smaller ones are either never found or simply ignored by most vendors. So seeing as most individuals for sale are immature females, that pretty much throws breeding them out the window.

However, even if you happened to buy a mated, mature female, or by some miracle got a male to mate with one of your females, and then got said female to lay all 200+ of her eggs, you'd be back to issue #1, diet. The resulting larvae are very small and a lot weaker than the large larvae sold by most vendors, and do not have the resistance to starvation that larger larvae have, so unless you have an adequate food source available for them, they'll be dead within three weeks, (at least that's what happened to Wong's wild egg hatchlings).

Platerodrilus foliaceus. Image courtesy of Nicky Bay

















Issue #3) Threatening Wild Populations:

So, let's say that you aren't much disturbed by the first two issues, as you don't plan on breeding your Platerodrilus and just want something pretty to look at for a while, even if it's rather short lived. Maybe you just want a lot of attention from jealous hobbyists by posting beautiful pictures of your new trilobite beetles, to boost your reputation as a "breeder" and get more followers. Maybe you just think all the Platerodrilus experts out there are wrong and that there must be SOME way to breed them in captivity.

If that's your mentality, then there's one last thing I can mention that might change your mind, and that is that all known Platerodrilus species have very limited ranges, as many live in isolated areas and are unable to disperse to new ones, on account of the females being flightless. They do not actually appear to be protected under any conservation laws yet, but that is likely due to lack of proper research, and will probably change at some point in the future.

Limited ranges mean a limited population size, and that automatically puts these at high risk from habitat destruction, as many Platerodrilus are mostly found in very pristine rainforests, (though some can also be found in disturbed secondary forests, Nicky Bay pers comm). They are also at high risk from, you guessed it, overcollection. Every time you buy trilobite beetles, you are supporting the collection of these species with limited population sizes, and are doing nothing to help them be preserved in captivity, as believe it or not, issues #1 and #2 of this post are true and very large husbandry obstacles, and the information provided above is based on the knowledge of people far more experienced with this genus than you are.

Platerodrilus ngi. Image courtesy of Nicky Bay

















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Honestly, writing this article was a little hard for me, I mean look as this blog, I'm all for breeding invertebrates in captivity, even very rare or legally questionable ones, as I think that getting species established in culture via captive breeding is one of the most important things we can do towards conservation of said species, even if it takes a few tries to find out their proper husbandry needs.

However, we now know most of what Platerodrilus feed on, and if we can't provide a proper diet for these things, the most FUNDAMENTAL part of any animal's husbandry, then I just don't think they should be kept in captivity. Who knows, maybe a zoo or something would be able to cultivate the micro flora and fauna needed to feed Platerodrilus, but I really don't think any hobbyists will be able to do it, they just don't have the resources needed.

Anyway, I hope this post proved informative to at least some hobbyists out there, this is different from my usual content on this blog, but I feel like this is an issue that needs more attention.

Many thanks to Nicky Bay for letting me use his beautiful Platerodrilus pictures, check out his Flickr here for more amazing wildlife photos!

Well, that's it for this post, thanks everyone for reading, see you all next time! 😉