Life isn’t always fair. Some individuals are simply born more attractive than others. In most cases the females are the choosy ones, whereas males will try to mate as much as possible. So being unattractive poses the largest problems for males. In many species, males will present the female with a gift (food), because, while she is eating she doesn’t mind having sex. However, the amount of food given is not equal between males. In the scorpionfly, unattractive males might not get a female quickly, but once they do, they sure know how to keep her around for a while!
The scorpionfly is aptly named scorpionfly due to the scorpion-like tail of the males, which they use to grab hold of the female during intercourse (see pictures below for the tail). They might look a bit terrifying to some people, but they feed on other insects and are not dangerous to us. Male scorpionflies “call” females by emitting long-range pheromones. Once they have attracted a female, they engage in long premating associations characterized by male wing and abdominal movements with sometimes brief genital contact (a sort of dancing). Finally, the male produces a salivary mass (spitball) which initiates copulation. The female will eat the spitball, once she has finished the spitball, she’ll fly away. So the bigger the spitball, the longer the mating!
This sounds all simple enough. However, scientific research to a particular species of scorpionfly (Panorpa cognata) showed that it is not as straight forward as that. A scientist by the name of Leif Engqvist found some interesting things by studying these critters. He basically started by catching scorpionflies and then staring at them for more than 6 hours a day! He found that while some males almost immediately jump the female when she arrives, others dance around with her for more than 6 hours! So why would some wait so long before closing the deal while others will close the deal almost immediately? Leif found that females are more likely to mate when the dance takes longer (Engqvist and Sauer 2002). As the production of the salivary mass (spitball) takes energy, it is costly to waist when the female leaves without mating. So if you only have one spitball, you better make sure that when you give it to a female she will be willing to mate! However, some males are in much better condition and are able to produce multiple spitballs, so they do not mind taking the risk that she flies away before mating.
The casanova of scorpionflies
Not all males are equally attractive. When a male starts “calling” to attract a female, it can take some time before a female arrives. However, the time it takes for a female to arrive varies greatly! Some males attract a female within a couple of minutes, but some take 6 hours before they are able to attract a female (Engqvist 2011). Furthermore, the time it takes a male to attract a female is heritable. Which means that some males are simply more attractive than others. The attractive males have larger salivary glands (spitball producing glands). However, the more attractive males produce smaller spitballs, which means they can only have a quickie (remember, the female leaves as soon as she finished eating the spitball). If they have such large glands, why would they only produce small spitballs while the unattractive males with small glands produce large spitballs? This is likely because attractive males can attract another female quickly and by producing many small spitballs they can have sex with lots of females. The unattractive male is less likely to attract another female anytime soon, so once he does manage to attract one, he tries his best to make it count. He dances around with her for hours and gives her all the spitball he can come up with. Female scorpionflies mate with multiple males, so not all her eggs are fertilized by the same male. Attractive males fertilize a few eggs with many females, but unattractive males do all they can to mate as long as possible with one female and try to fertilize as many eggs as possible with her.
So which tactic will work best? It will depend on the quality and attractiveness of the male. Attractive males might get the most offspring by slutting around as much as possible. Unattractive males can try, but will utterly fail and are better off when treating one girl right.
1) Engqvist and Sauer (2002) Amorous scorpionflies: causes and consequences of the long pairing prelude of Panorpa cognata. Animal Behaviour 63: 667-675
2) Engqvist (2011) Male attractiveness is negatively genetically associated with investment in copulations. Behavioural Ecology 22(2): 345-349.