The concept of parents looking after their babies is easily recognisable. We were all cared for when we were younger (even if not by our biological parents); fed, clothed and housed. We recognise the same urge when we see a cat cleaning her kittens or a bird collecting nest materials, but do we see it in insects? Well, more than you might think.
Only about 1% of insect species show parental care; selection pressure favours lots of offspring, effectively limiting parental care to species which produce fewer young. Parental care can mediate the transition from solitary to group or family living, both for an individual and on an evolutionary scale. It is likely to have developed as an altruistic trait to enable parents to better ‘pass on their genes’ by improving the survival of their offspring, even at the cost of their own energy, food, or even future reproductive opportunities. It may be evolved in environments with high selective pressures such as predation risk or reduced food availability.
Some insects show pretty much every level of sociality that you can think of, so here’s a walk-through of what insect parental care looks like. Through egg care, larval care by one of both parents., and the formation of family groups, this is the insect guide to good parenting:
In some species, parental care starts before the young even leave the egg. Female earwigs groom their eggs to remove harmful mould spores and secrete symbiotic bacteria onto the larvae which are both antibiotic and anti-fungal. One study found that only 4% of European Earwig (Forficula auricularia) eggs hatched when they were left untended, as opposed to 77% for tended eggs. Mothers do the bulk of the offspring care but for some species the father takes the burden.
Male water bugs (Belostomatidae) brood the fertilised eggs on its back until they hatch. Carrying the eggs around makes the males more vulnerable to predation and hinders their foraging, making a large energetic expense to rear their offspring. It also stops the male from being able to mate again until the eggs have hatched.
Potter wasp (Eumeninae) females build small clay nests for their larvae, bringing them food, defending them against predators, repairing damage and cleaning debris from the nest. Males play no role in the larval care but do patrol nest sites to find females to mate with.
Biparental larval care
Burying beetles (Nicrophorus spp.) take it up a level with both parents caring for their brood. Not only do they stock their larvae’s underground nest (or ‘crypt’) with a decomposing carcass (yum), but they also feed them regurgitated meat if begged. If there isn’t enough carrion to go around, parents will cull the most demanding larvae; whilst this might seem harsh, it ensures the survival of their less needy siblings. Although the parents don’t form the monogamous pairs often seen among vertebrates, they will stay together until their larvae reach adulthood.
Cockroaches might not initially seem the most likely parents given their occasionally cannibalistic tendencies but show some of the most comprehensive parental care of the insects. The females of some species are viviparous, gestating their offspring under their wings and producing a protein and carbohydrate rich ‘milk’ to feed their young nymphs until they are old enough to be ‘born’.
Both cockroaches and burying beetles, unusually for insects, form family groups. In cockroaches this is because nymphs need to receive the gut protozoa essential for digesting cellulose from their woody diets. They lose the protozoa after every moult meaning that to ensure the nymph’s survival the adults have to stay with their offspring until they reach adulthood.
It is thought that this feeding was the key which allowed ancestors of modern termites to become eusocial. Termites are very closely related to cockroaches and these family groups expanded and evolved to become eusocial colony organisms. Living close together with millions of their ‘siblings’ allows termites to be sure of security and a food supply and allows traits like monogamy, foraging and nest inheritance to be developed. The switch from parental to sibling care is thought to have led to social behaviour forming in ants, wasps, and bees.
Evolution of sociality
But what is the glue holding these parents to their offspring? It’s surely not the big eyes, fluffiness, and helplessness that draws us to babies, kittens, and ducklings- even entomology students would struggle to call a cockroach nymph cute. It seems insect ‘families’ are reliant on pheromones as a recognition mechanism. Earwig nymphs’ pheromones reflect the quality of the food they’re being given to influence their mother to provide more food if needed. Cockroach nymphs use similar pheromones to aggregate with their parents and siblings and are able to distinguish non-siblings.
Brood care is thought to also have driven formation of families and social groups in vertebrates. The evolution of parental care in insects can be a model for the evolution of parental care in birds, fish, and of course mammals. It seems that you might have a lot to thank cockroach milk for your survival to adulthood.