If you ever see a cockroach with a lump attached to its abdomen, it’s a female protecting her offspring, as they have been doing for millions of years. Most of these insects create special capsules, called oothecas, where they carry their eggs until the nymphs hatch and become independent of their mother. A study published in 2018 found ootheca fossils in northeast China that were more than 115 million years old.
Parental care in insects is not only ancient, it is also incredibly broad and diverse. It has evolved many times to deal with different threats and takes every imaginable form. In this article we are going to learn about some of the most striking examples.
As ectothermic animals, insects cannot generate their own heat, and one of the main challenges they face is surviving in harsh environmental conditions. Given that future weather events are likely to become more extreme due to climate change, it is vitally important to understand how parental care can be a buffer against variations in ambient temperature.
There is a species of burying beetle (Nicrophorus vespilloides), widespread in the northern hemisphere, breeds on the carcasses of small vertebrates. When the larvae hatch, they feed on the carcasses and continue to benefit from parental care. A research group discovered that, without the care of the females, the larvae of this beetle manage to survive at a temperature of 20°C, but not at 15°C, which they do with care. The authors believe that this may be due to the competition that is established at this temperature between the larvae and the microorganisms. In other words, with their care, the mothers control the populations of microorganisms, and this means that their offspring can live at lower temperatures.
The burying beetle not only helps with the cold temperatures, it also feeds its larvae by regurgitating carrion when they cannot yet eat it directly. When the carcass is too small to feed them all, they eat a few.
These two cares are reminiscent of birds that incubate their chicks and bring them food, but there are other insects that have a style more similar to that of mammals. The cockroach Cryptocercus punctulatus It feeds on wood, and as the nymphs are not yet able to process it directly, they drink the intestinal fluids of their parents, resembling suckling pigs. This allows the young to acquire the intestinal flagella necessary for the digestion of cellulose.
The Wolf of the Bees (Philanthus triangulum) is a species of wasp that is not named by chance. Females hunt bees, paralyze them, and take them home to feed their young. The young are kept in warm, humid cells, so there is a high risk of food spoilage. To preserve it, the mother applies chemical secretions that reduce fungal growth.
Sometimes, just giving food is not enough, and that is because cuckoo flies (Miltogramminae) are not named by chance either. Like the cuckoo, they lay their live larvae in other people’s nests – in this case, wasps’ nests – which kill the immature wasps and eat the provisions. To prevent this, mother wasps make regular visits to their nests not only to provide food, but also to clean them of fly larvae.
But the most extreme case of provisioning is perhaps that of the humpback earwig (Anechura harmandi). Nymphs kill and eat their mother before leaving the nest. These mothers do not attempt to escape cannibalism or produce a second brood if isolated from their nymphs. This is simply a case of compromised parental care.
In some insects, parenting can be so laborious that both parents are required. The aforementioned burying beetle is monogamous, with both mom and dad helping with parenting. She usually does the feeding and he does the guarding, although both defend their young by cooperatively attacking intruders. These are usually other burying beetles, as infanticide is common in this species.
Another well-known case of biparental care is that of the Australian rhinoceros cockroach (Macropanethia rhinoceros), the world’s largest cockroach. Both adults mate in the burrow and feed their young with leaf litter and excrement that they collect together. This animal is so curious that in Australia it is sold as a pet to observe this joint breeding, and there are guides on how to care for your giant cockroaches.
At this point, we cannot fail to mention the famous communal breeding of bees, ants or termites. In the case of another giant Australian insect, the termite Mastotermes darwiniensisThe king and queen produce excrements with which they feed their hard-working offspring so that they stay in the nest and help them with household chores.
Less known is the behavior of the bed bug Elasmucha griseaThey are often attacked by predators such as ants, which devour their eggs ferociously. As unity is strength, several females join their clutches to defend it more effectively.
Other female bed bugs (Gargaphia solani) lay their eggs in the nests of a relative and then leave them alone. This does not seem to be a case of parasitism, as it benefits everyone. On the one hand, the bug that has laid the eggs does not have to invest energy in caring for them. On the other hand, a study showed that the clutch of the individual that has had the extra eggs snuck in is more likely to survive because, like sheep grouped together, if a predator comes along it will eat a smaller percentage of its own eggs.
Finally, some insects relegate parental care to another species. This is the case of the membracids (Membracidaenot to be confused with aphids which are Aphididae), small insects that suck the sap of plants and transform it into honey. The females lay their eggs on leaves and take care of their young when they are born, but in the presence of ants they abandon them and go on to produce new broods. A study showed that the ants protected the young from predators and, in exchange, fed on their honey when they were older.
Because of their great abundance and diversity, insects are an ideal model for investigating the evolution of parental care. However, it is curious how little we think of them when we refer to this type of care.
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