2020

Get to Know Birch Parent Bugs!

Who lives in forests, forest edges, groves, parks, alleys and prefers to live on deciduous trees, most often, birches? This time, nature researcher Ilmārs Tirmanis introduces an insect that is very common and is relatively frequently to be spotted in Latvia – birch parent bug (Elasmucha grisea), which feeds on tree sap.

From the first sight it looks just like a common bug

The length of an adult insect reaches less than 9 mm. Males visually differ from females not only by their smaller size, but, of course, also by the shape of their genitals and also by the colour of their tentacles (male tentacles are black, female – dark brown). Moreover, male life expectancy is shorter. Their duty is more modest.

Parent bugs of both sexes spend winter in the adult (imago) stage. In spring, the mating process takes place, after which the males pretty soon leave this world, but females have to live for quite a long time.

Baby care

Almost half a thousand different species of insects of this order represent shield bug fauna in Latvia. So why has the birch parent bug earned the honour of being specifically mentioned here? The reason is the peculiar instinct of birch parent bug females, which makes them take care of their offspring. It seems obvious to us humans that mammals and birds take care of their younger generation. But if insects act like this?

At the beginning of summer, birch parent bug females lay eggs in birch leaves (usually on a mature tree) and, guided by their mother's instinct, spread their legs wide, standing above them, trying to cover the eggs with their body. However, it would not be correct to compare these insect females with hatching bird females, since they do not warm their eggs but only protect them from potential enemies.

Each guarding mother spends the entire egg development period covering them.

Hatching eggs slowly turn into nymphs

Birch parent bugs develop with incomplete transformation (no larval stage); for this reason, their young generation should be called nymphs, not larvae. These nymphs go through five stages of development.

For the first few days after hatching, the little nymphs crowd tightly under their mother, where they eat their eggshells, thus absorbing specific bacteria that are very necessary later in life, and gathering strength. If some baby dares to separate from the group of siblings, the mother leans in the direction of the refugee and stretches the tentacles to push it back to the others.

Later, the nymphs spread more and more all over the leaf of the tree, but do not distance themselves from their mother, so that in case of danger, they can run back under their caretaker.

A few weeks after hatching from the eggs, nymphs are still being watched and looked after. They also get away from their native leaf, but the mother regularly walks around to gather her children together in a close circle.

Both adult birch parent bugs and nymphs lust for birch sap, which is why females choose adult tree leaves for laying eggs.

When nymphs are in the active feeding phase, they regularly move from their leaves to the buds and back. The mother regulates the movement of children with the touch of her tentacles. This technique of care helps until the end of the stage three of nymph development.

Nymphs that run around and keep contact with other family members tend to form mixed offspring communities. Their mothers do not object and are ready to protect these self-created “kindergartens” of their children.

With stink glands against enemies

Child protection techniques that are typical of birch parent bug females include a number of behavioural patterns, the most significant and effective of which are the spreading of the wings, trampling of the body, and leaning against the enemy. Methods of protection (both for children and their own) also include unpleasant odour secretions from the abdominal stink glands, which is characteristic of several shield bug (and stink bug) species. But the stink gland does not always protect even the females themselves. And there are so many who want to eat them…

If the mother dies, the nymphs who previously went to the “kindergartens” are bit more fortunate than their siblings, because they will be protected by the foster mothers in the future.

As the new generation develops, and time passes by, the nymph family gradually splits into smaller groups, until finally, at the end of the third stage of development, it completely disintegrates. If everything went smoothly, the mother's worries are over now. And her life soon comes to an end …

However, the process of dispersal of the new generation can be asynchronous, jerky, because the birch parent bug nymphs of one particular lay tend to develop (change generations) unevenly. In such case, the mother is not able to perform her duties effectively enough.

The new generation of birch parent bugs reaches the adult stage in the second half of summer, the majority of them in August.

Similar to birch parent bugs, birch-conifer shield bug (Elasmucha fieberi) females also provide attentive care for their offspring, these species are less common in Latvia but also less selective as to their place of habitation.

However, a person who wants to observe the maternal behaviour of insects in person, does not necessarily have to go to the forest to look for shield bugs of the genus Elasmucha. You can be lucky just by walking to a currant bush in your garden, because the female shield bugs of Elasmucha ferrugata also take care of the younger generation for some time of their lives.