Unless you have been hibernating under a rock (like many beetles at this time of year) you will know that today is the most romantic day of the year, St. Valentine’s Day, an opportunity to show that special someone how much you care, to lavish gifts, to make public displays of affection and to perhaps find true love…
In the beetle world, love is everywhere (well, not as we know it, but you know!)
For instance, one of my beetle loves is the soldier beetle, Cantharis rustica, who, rather than wearing its heart on its sleeve, wears it on its pronotum instead! Here is a ‘his and her pair’ from the Museum’s collection – can you make out the heart?
These beetles are predatory on other smaller flower-loving insects and can be seen from spring wandering about on umbellifers such as cow parsley.
Also within the Cantharidae family (the soldier beetles – so called for their general black and red smart appearance resembling a soldier’s uniform (use your imagination!) is what is lovingly termed ‘the bonking bug’ or more scientifically Rhagonycha fulva. These beetles have worked hard at their reputation and can be seen in the UK from late June to late August bonking away, in fact they can’t get enough of it! They too can be found in large numbers on umbelliferous plants feeding on pollen and nectar but also predating on other insects.
The Cowpea weevil, Callosobruchus maculatus adds weight to the terms ‘love hurts’ or ‘a thirst for love’. The male of the species has a specially adapted penis which ‘spurs’ the female, damaging her internally. This adaptation is thought to act as an ‘anchor’ for the male and also puts the female off mating for a while which confers a competitive advantage to the mating male. However, the female endures, as she is thirsty – what a gal will do for love! These beetles feed on stored pulses which contain no more than 10% water. Without access to an additional water source, the females use the males’ ejaculate to quench their ‘desire’ as it were. The ejaculate makes up 10% of the males’ weight and so is a high energy investment but this is okay because once the deed is done, the females lose interest anyway (isn’t this usually the other way round!)
Callosobruchus maculatus penis
In the burying beetle, Nicrophorus defodiens all is not fair in love and war. When the male secures the romantic gift of a large decaying carcass for his love to feed on, the resulting offspring from this monogamous pairing will not be able to consume the whole of this plentiful resource. This gives the male an excuse to look for more than one female mate, meaning their coupling produces more surviving offspring than he would by remaining monogamous. This is not good news for the monogamous female, whose reproductive success decreases with the introduction of a rival female, but, she puts up a fight, using her feminine wiles, or behavioural tactics, she interferes with the males’ pheromone emissions and thereby decreases his success at attracting another female. This ensures that she keeps her man (beetle) all to herself!
Nicrophorus defodiens in the Museum's collection looking rather pink!
Max Barclay, head of Coleoptera Collections has this to add about the weevils, which can be seen in all their carnal glory in the Museum's most excellent exhibition Sexual Nature http://www.nhm.ac.uk/visit-us/whats-on/temporary-exhibitions/sexual-nature/index.html
"Of course, size isn’t everything, so look no further than tiny weevils for some bizarre mating practices – especially perfecting the clingy boyfriend.
Once the male has a female, he doesn’t let go, he’ll stay on her back for up to a month and mate throughout. The more males she’s been with, the less chance of a single father and, of course, each male wants to pass on their genes, so this is his way of preventing her mating with others. This is known as 'mate guarding'. Mating weevils still go about their daily business while attached, including eating and even flying!"
Here are an ungainly pair of mating weevils of the genus Lixus, the same genus featured in the Sexual Nature Exhibition
These are just a few examples of the complexities of mating in the coleoptera, that are too numerous to mention here.
Happy St. Valentine’s Day!