RSPB Trainee Ecologist Kirsty Godsman explores the parenting skills of insects after finding out some fascinating facts about carrion beetles.
Do insects make good parents?
Last month, I discovered something fascinating about a closely related group of species commonly known as the carrion beetles or Sexton beetles (all belonging to the genus, Nicrophorus). This is a group of beetles that anyone with a moth trap might be familiar with as they are attracted to light. But if you have never come across them before, here is a photograph of one of the 6 species that occur in the UK.
Nicrophorus vespilloides (www.eakringbirds.com)
At first glance, these beetles may seem a little gruesome. They are known as carrion beetles because they feed on carcases as adults and larvae. As a result of this association, they can be covered in mites and usually smell unpleasant. However, delve a little deeper into the lives of the carrion beetles and you might find yourself warming to them.
In order to find a mate, adult beetles must find the carcass of a small vertebrate. This can be a difficult task in itself as it is a very limited resource. Once a carcass has been located, they will then need to fight off any competitors. Once there is only one male and one female left, they remove the hair or feathers of the carcass and bury it in the ground. This is an incredible feat for something that is no bigger than 3cm. What is possibly even more amazing is that, if the ground is unsuitable for digging in to, they will drag the carcass to a more suitable substrate. They will also form a sphere or brood ball with the carcass, onto which they secrete a liquid which is thought to preserve it. The female then excavates a corridor from here where she will lay her eggs.
Then it gets really interesting.
At this point, the male and female wait for the eggs to hatch and continuously guard the nest from predators and competitors. Once the eggs hatch, the males of some species leave but the rest continue to guard their nest. The females begin provisioning the brood and will not leave until her offspring have left. Initially, the female has to lead the newly hatched larvae to the carcass by “chirping” or stridulating her wing-cases on her abdomen. She then must feed her young directly by regurgitating. It has been suggested that many species must do this after every larval moult or the young will never make it to adulthood.
Although the circumstances may seem grisly, this behaviour is far more sophisticated and complex than most people would expect from an insect. However, they are not the only insects to provision their offspring in some way. For example, the tiny pot beetles (Cryptocephalus species) build a case for each egg that they lay which prevents predation of their offspring. It is very common for herbivorous beetles such as leaf beetles and weevils to lay their eggs on the larval host plant so that, as soon as they hatch, the larvae are able to feed. Some weevils even go as far as to roll a leaf up to protect their eggs. The care provided by Nicrophorus mothers, however, is the most involved of any non-social insect.
RSPB Trainee Ecologist Genevieve Dalley tells us about her discovery of a new flying insect species for Scotland.
A new species for Scotland
In June this year I went to RSPB Insh Marshes in search of freshwater invertebrates. And I wasn’t disappointed! Amongst a wealth of interesting and local species was the star: Molanna angustata, a new species for Scotland.
Sometimes the most unassuming little creatures can turn out to be the most interesting. A small, pale brown caddisfly with long antennae; Molanna angustata would normally be one of the first to escape a moth trap unnoticed on a sunny morning. But a closer look will reveal a sweet little insect with an interesting story.
In Britain there are 2 species of Molanna: Molanna albicans and Molanna angustata. M. albicans is a species largely associated with small lakes. It is found in Ireland, Wales, 2 sites in West Yorkshire then, after a big gap, scattered sites in Central Scotland northwards. M. angustata, on the other hand, is a species of lowland lakes, ditches, ponds and canals. This is fairly widespread across lowland England and Wales, up to the Lake District and Yorkshire. However, it has never before been found in either Ireland or Scotland. The two species have never been found together in the same place.
Molanna albicans distribution
Molanna angustata distibution
In order to identify caddisfly adults to species, the genitals and wing patterns must usually be inspected under a microscope. And it was to my surprise when sorting caddisfly specimens taken from the ‘moth trap’ at Insh Fen that I had two male Molanna, both matching the features of Molanna angustata.
Molanna angustata adult
This was exciting as, looking at the current distribution map, this would only be the second record for Scotland. I sent the specimen to the National Recorder for Caddisflies, Ian Wallace, and it turned out to be even more exciting: the ‘first’ record (Rannoch Moor, 1900) turns out to have been a mistake – a check with the museum revealed the specimen does not exist and was probably a data entrance error. This makes the Molanna angustata I found at Insh the first ever record of this species in Scotland.
Molanna angustata male genitals
This discovery raises more questions than it answers: why has it never before been found in Scotland? Is the species moving north or has it simply gone unnoticed until now? What habitats is the species truly associated with?
There has been a number of examples in the invertebrate world in recent years showing the move of southern species northwards (e.g. Southern Hawker Dragonfly) potentially at the expense of specialist upland species (e.g. Upland Summer Mayfly). Is this the case with the Molanna species? However, this still wouldn’t explain the jump from the current distribution all the way up to Insh. Further investigation is clearly required.
Finding Molanna angustata has reinforced to me the excitement, interest and importance of investigations into understudied species. Whether moth trapping for caddisflies or kick netting in upland streams, you never know what is going to turn up next. There is so much to discover and learn and I couldn’t recommend it highly enough!