Insect Eggs - What do we know?
Introduction – When it comes to reproduction strategies of animals, there has been much research done into different life cycles – live birth, egg laying, mating practices, etc – but one area that is often overlooked is the insect world. With insects being a such wide grouping of creatures, there stands that there is much research still to be done. One area I find interest in is insect eggs. Have you ever wondered why insect eggs all look so different? In this short essay I want to briefly touch on the interesting way bugs lay their eggs, discussion on how these eggs vary in characteristics, and finally look at some recent studies showing why these eggs all look so different from each other.
Methods of laying – Insects begin their reproduction cycle in a similar way to most animals – become sexually mature, find a mate, breed, and develop eggs that can then be laid. The difference that comes from this step is the method of egg laying that female insects possess. Female insects possess a body part called an Ovipositor which is a long needle-like appendage on the back end of her body. This body part is used slightly differently depending on the insect species – for example, many wasps species use this Ovipositor as a piercing tool as well as an egg laying device. Wasps will sting their prey with this Ovipositor as well as dig into wood to hide their eggs inside (Sezen). Some other examples of differing use of this Ovipositor would be Sawflies using it to open plant tissue for egg laying or grasshoppers digging into soil to lay these eggs.
Differences in appearance – Insects lay eggs in many different ways – location, size, color, shape, and more are all fairly unique to an individual species. “Eggs can be laid singly, in clusters or in specialist structures called oothecae” (AES). You may find a group of insects that all lay similarly colored round inconspicuous eggs, while other groups of bugs have eggs that are entirely distinct to them and them alone. For example, the photo below is an image from National Geographic showcasing a wide variety of different eggs from Stick Bugs. In addition to the variety of egg shapes you can find, you will also see the amount of eggs vary by species/group. “Although lifetime fecundity varies from less than ten to several millions of eggs, most insects lay between one or two hundred and a couple of thousand eggs (Hinton 1981)”.
Explanations for differences – So why are these differences present in eggs? Is it purely cosmetic or does their differences serve a purpose? There is no fully agreed upon answer yet – as mentioned above, this is an area of study that has a long way to go, but that doesn’t mean there aren’t some current theories. One theory is that insect eggs use a form of mimicry. There are some species of lepidopteras that have observed laying eggs that resemble emerged parasitic galls – these eggs would look fairly unassuming due to this allowing for a lessening of predation. Another thought is that egg size explains insect adult size – though this has been disproven as a false observation (Church). What size has been involved in though is masquerading as other objects. There is evidence for eggs using a masquerading technique to appear as a dew drop, a seed, or even as plant organs (Grenier). Color of these eggs have been observed to change based on their environment to better blend in as well (example below) (Holmes).
Conclusion – This is just a very short look into the world of insect eggs – sadly, this topic has much to be explored and lots of questions left to be answered. What we do know if a great starting point and is enough evidence to tell us that insect eggs are specialized for their unique circumstances, even if we don’t fully understand them completely yet.
https://entnemdept.ufl.edu/walker/ufbir/chapters/chapter_18.shtml#hinton_1981
https://naturedocumentaries.org/3843/giant-ichneumon-megarhyssa-macrurus-ovipositing/
https://www.biorxiv.org/content/10.1101/471946v1.full.pdf
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