Where Do the Glass Lizards Go? – Scrutinizing the Seasonal "Disappearance" of Pseudopus apodus | Articles
By Plato Stefanopoulos
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| Adult Glass lizard from Eastern Macedonia (C) Stamatis Kalogiannis |
On my first ever herping session outside of the Athens
Metropolitan area in Early May 2020, it was first revealed to me (in the form of
several misses and DORs) – glass lizards are a very common reptile in Greece.
On my first “herp trips” in South Euboea in June of the same year, I also saw at
least 5 more living individuals and several more dead ones. Considering the
above, I came to the premature conclusion that this would very likely be the
case throughout the active season, and boy was I wrong! On my revisit to South
Euboea in mid-July, I only found two glass lizards in over 10 days of carrying
out similar hikes to the ones I was in my previous visits. And they seemingly completely
vanished in August. Why was that?? The answer is, we don’t know!! – mostly. In
this unserious article, I will attempt to present all
available information I have regarding the life history of glass lizards, from
both the internet and the field, and try to come to a conclusion regarding the
reasons for their perplexing activity patterns.
The explosive activity of Pseudopus in spring, their “disappearance”
in mid-late summer and the lizards’ subsequent (underwhelming) reappearance in
fall have been puzzling herpers and herpetologists for decades, and I have
taken it upon myself to try to reason with the facts (from the field and the
internet) to come to the most logical conclusion. While most other species of
reptiles see somewhat similar seasonal drops in observation frequency, few have
them to a degree as… extreme as that of the glass lizard. Here, I present some trends I
have seen in 2021 and 2022:
- Spring 2021: I probably saw more glass lizards than I did snakes.
- Fall 2021: I saw a few roadkilled individuals in the Peloponnese after the rains. The spot where I routinely see 10 individuals per day in the spring, only had one when I visited it.
- Spring 2022: I saw a ridiculous number of them.
- Summer 2022: large numbers of them stopped being posted in the start of July, but they are still being observed somewhat consistently (once every few days) in August.
Upon considering all this (unreliable) data, I have come to formulate 3 major hypotheses as to why the activity of Pseudopus is as it is:
1. THE REPRODUCTION HYPOTHESIS
It is well-established that the reproduction of Pseudopus
takes place in April-May, which also happens to be the time when surface
activity reaches its peak. The idea is that during that time, there are several
additional activities that require them to be out and about more often,
excluding feeding and finding refuges (searching for mates, fighting rivals,
looking for nesting sites, etc) and since more energy is expended by these actions,
feeding increases as well, and hence there is even more activity. As a result,
after mating concludes, females disappear in their nests, coiling over their
eggs until they hatch, and males may also find themselves in months of
inactivity as they have lower energy requirements. The added activity burden of
sexually mature individuals could be the reason why juveniles are observed less
frequently than adults throughout the year and they don’t have a distinct peak
(excluding hatchling dispersion in fall). However, almost all reptiles have the
same patterns in yearly observation frequency, but not to such an exaggerated degree,
so it simply cannot be the only factor for their disappearance.
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| Large adult male with breeding colors, Evros prefecture, May 2022 (C) Plato Stefanopoulos |
2. THE WET YEAR HYPOTHESIS
As snails form such a large part of a glass lizard’s diet, it is thought by some that the lack of humidity in the summer drives the glass lizards to aestivate as their main prey does the same. In my opinion, this does not seem to be valid, as most of the time, glass lizards will predate snails “in their sleep” on warm sunny days, and even when not considering that, glass lizards also eat a multitude of other prey items, like beetles and grasshoppers, which (along with sleeping snails) are very plentiful throughout the summer. My theory is that humidity plays a more vital role – maybe they cannot operate well in extremely low humidity conditions and are more prone to and in severe danger of dehydration, and perhaps, most individuals may aestivate until conditions are more favorable. This could also potentially explain why the mass disappearance seemed to be somewhat less pronounced in wet years like 2020 and 2022.
3. THE PREPARATION HYPOTHESIS
This idea is not entirely my creation and I think it is the one
that probably contributes the least to the disappearance, but it sounds
interesting on paper. Either way, glass lizards can often be observed basking
outside refugia in in spring and very early in the summer in the cooler hours
of the day, and this is performed to prepare themselves for activity. This
claim may be a longshot, but the start of the apparent inactivity period in the summer essentially
coincides with the warming of the nights each year. The idea is that it is possible
that since A) they do not need to come out in the open to bask due to high temps
and B) movements over large distances are not necessary due to the end of the
reproductive season, they do not frequent open areas and even if active they go
unnoticed, perhaps moving only deep inside thicket-type vegetation. In any
case, while this may sound convincing at first, I do not think it’s plausible as
I believe that observation frequency would be significantly higher, as there would have to be more "stray" individuals in the open, and I favor
an aestivation hypothesis instead of this.
Closing remarks
So, what is the verdict? Personally, I think that the most
likely scenario is that we can blame all 3 hypotheses (well, mostly 1 and 2)
for the disappearance of glass lizards, and I am almost 100% certain that aestivation
occurs to some extent. However, we can only be certain if we track individuals
directly, though research like this is often frowned upon, and for good reason
(biased results, harmful to the animals, etc.). I figure that this activity
halt will remain unstudied for many more years along with several other enigmatic aspects
of the species’ life history: is the population really 80% male and 20% female?
Are there really more males than females, or is the spread even and it is entirely
sampling bias, with males being in positions where they can be captured more
often? Why are juveniles so hard to find?? We don’t know! And that’s a huge
part of what makes these weird and unique lizards even more fascinating.
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| Juvenile, Attica, March 2022 (C) Charis Kouelis |