The egg-cellent world of invertebrate eggs

7 spot ladybird - Jon Hawkins

This time of year, eggs are often on people’s mind but usually of the chocolate variety and we wanted to take the opportunity to talk about some of the incredible eggs and egg laying behaviours that can be seen in the invertebrate world. Our Wild Learning Officer, Lucy explores further.

Cheesy-pig, rolly bug, bibble bug, monkey pea, chisel-pig, slater, Jonny-grump, woodlice have no less than an amazing 176 different nick names.  

In the UK we have around 37 species of native or naturalised woodlice and these characterful crustaceans can be found in damp and dark places such as amongst leaf litter, decaying wood, under stones, paving slabs, in walls and compost heaps.

It’s not just their array of nick names that make these invertebrates so interesting however, the females have a unique way to carry their eggs in order to increase the chances of their survival as woodlice mortality is high, with only a few in each brood surviving to adulthood.

During the mating season, female woodlice start to develop a water filled brood pouch and once they have mated, the female carries her fertilised eggs in this pouch where a whooping 50 or so eggs stay and are carried and protected by her. If you happen to be looking at the underside of woodlice and would like to test your eyesight, you may notice the female’s orange tinted brood pouches and the tiny eggs inside them. The eggs will develop for 1 – 2 months before they hatch and remain in their maternal pouch until they are big enough to survive independently. If you time your observations right, then you may just notice tiny white, grey, or orange-coloured woodlice within the female’s pouch. It’s quite a spectacle to see. Most species of woodlice have a breeding season between April and October and can produce two generations per year, so keep an eye out for them within this window.

Ladybirds, a gardener’s best friend due to their impressive aphid eating ability, have broods of up to 40 eggs and can have more than one brood a year depending on the species of ladybird.

These polka dot invertebrates are strategic when it comes to their mating and egg laying positions. The criteria for a suitable mating and egg laying spot is simple, it must have an aphid supply nearby so that when their eggs hatch their hungry offspring have dinner already served. Although often this time of year it is easy to eat our own body weight in chocolate eggs, a ladybird larvae’s survival depends on eating their own body weight in aphids, making the parents' mating and egg laying location an important decision. If only we had the same excuse for Easter eggs, and our survival depended on it too.

It is also thought females will lay some infertile eggs in the brood as a back up plan in case the ready-made meal of the aphids is in short supply once her viable eggs hatch. Taking between 4 – 10 days to hatch, the young will feed on the unhatched infertile eggs to tide them over if their on-tap aphid supply has been eaten. Look out for clusters of pale yellow to deep red ladybird eggs under leaves.

So, what about the aphids themselves. Although they get a bad press at times due to their plant stripping abilities, they are a vital food source for species and interesting in their own right, and we think they also deserve a mention.

Aphids are seemingly very organised invertebrates and lay their eggs in neat rows. When they are first laid, they are honey coloured and covered in a foul-tasting wax to put off any nearby species that are feeling peckish.

Like ladybirds, for female aphids it’s all about location, location, location when laying their eggs and they will lay them next to a readily accessible food source, which for a young aphid, is near new buds on trees.

Aphid eggs - Lucy Shepherd

Aphid eggs - Lucy Shepherd 

When it comes to testing to see if the location to lay eggs is suitable, it could be argued that butterflies have the most unique way of doing so as butterflies’ taste through their feet! Thank goodness they don’t have sweaty socks to contend with.

Butterflies have the ability to taste through their feet and this plays a very important role in their egg laying process. In order to make sure that they have selected a host plant that is a suitable food source for their caterpillar offspring, they sample to the location first by tasting through chemoreceptors in their feet. Anyone that has ever read 'The Very Hungry Caterpillar' and watched a caterpillar in action, will know that they have an insatiable appetite and spend their time munching away. If the female lays her eggs on a host plant that is unsuitable for her caterpillars to eat when they hatch, then the chances of survival are low. Luckily, females are able to store the male’s sperm until they are ready to lay their eggs once they have found a suitable plant.

There is great variation in the butterfly world and, depending on the species, butterflies can lay eggs individually one at a time, in clusters, or by the hundreds. If you are lucky, you may just see them in action laying their eggs. 

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