Scorpion flies – not as scary as they sound or look

I’m very fond of Scorpionflies, in fact, they are almost up there with aphids on my all-time favourite insects list. They, at least to me, are reminiscent of something that one would expect to find in Lewis Carrol’s Alice in Wonderland. They belong to the Order Mecoptera, which until some pesky taxonomists decided that fleas are Mecoptera, was one of the smaller insect Orders with just 600 species, if fleas are indeed Mecoptera then we now have 2600!

Male (left) and female (right) Scorpion flies. Despite the resemblance to the back end of a scorpion it is not a sting, but part of the male genitalia.

Ignoring fleas for the moment, there are nine families of Mecoptera, but only three are common; Scorpion flies (Panorpidae), the Hanging flies (Bittacidae) and Snow fleas (Boreidae) (Byers & Thornhill, 1983). Of these only two occur in the UK, the Scorpion flies and the Snow fleas. Adult Scorpion flies are mostly scavengers, mainly eating dead insects, topping this up with a bit of pollen, nectar and fruit juice and for a special treat, bird faeces. Their larvae live in the soil and mop up whatever dead things they come across.

The Snow fleas feed on moss and are only getting a mention here because they are quite cute and for a few years I held the record for the furthest north record 😊

Cute Snow fleas 😊

The Hanging flies are carnivores capturing live prey as adults and larvae and deserve a special mention as they (and although it shouldn’t, but it appeals to the ten-year old in me, makes me giggle) have a penisfilum.

Male (left) and female of Bittacus planus. Photo provided by Dr. Baozhen Hua. Note the knob in the male!

Anyway, back to the scorpion flies. They are found in temperate regions, worldwide and as of 2018 there were 280 species. The males are highly competitive, as are many of the Mecoptera. Males will fight over their food, which as I mentioned earlier is quite high in dead flies, which they often steal from spider webs.  They have no fear of spiders as they can dissolve the web if they do get caught.

Another cool thing about scorpion flies is that they, like some spiders, use nuptial gifts to increase their chance of mating. They first use a pheromone which as pheromones go, is pretty short range, 10 -15 metres. Once a female has been enticed by the pheromone, the males than flash their wings, which are striped and do a bit of a dance. Depending on species, what happens next could be one of three tactics.

Nuptial gifts and mating of Dicerapanorpa magna Photo provided by Dr. Baozhen Hua.

male gives female food which she eats during copulation either a salivary deposit from enlarged salivary glands or a dead insect, and waits female arrival.  Another tactic is to find a suitable dead insect which he then stands by, waits for a female to arrive, and then copulates with her while she eats it. Some males are less generous and will force themselves on a female without any presents or even pheromones, holding their chosen mate in place with his abdominal clamp (Tong et al., 2018). The size of the gift is related to the duration of copulation and to how long it will be before the female mates with a different male (Byers & Thornhill, 1983); females that were subjected to forced copulation have a very short inhibition time – the more the males invest in their nuptial gifts, the more offspring they sire. Basically, they get what they pay for! The eggs, usually no more than ten per clutch, are laid into damp soil.

When I introduce Scorpionflies to a new audience, I am, as I find frequently with other insects, faced with the usual human exceptionalism question “

“Mecoptera are most often defined by the characters they do not possess” Penny (2016)

They are not pollinators generally regarded as pollinators (thanks Jeff Ollerton for reminding me that some do visit flowers for nectar), but they are not crop pests and nor are they vectors. We don’t eat them and most of them most are not biological control agents. Bittacids are, however, predators. Panorpids are recyclers, they feed on carrion. The Nannochoristids could be seen as s bio-indicators; their larvae need clean water and Boreids could act as climate change ‘canaries’ because of their limited dispersal ability and their need for cold.

Scorpionflies have appeared in video games (Shelomi, 2019) so I guess are helping the economy and keeping people entertained.

In the long distance past (170 MYA), before angiosperms made their appearance and allowed the explosion in insect diversity possible, three groups of scorpionfly, now extinct, fed on the nectar of gymnosperms and in return pollinated them (Ren et al., 2009).

References

Byers, G.W. & Thornhill, R. (1983) Biology of the Mecoptera. Annual Review of Entomology, 28, 203-228.

Palmer, C. (2010) Diversity of feeding strategies in adult Mecoptera. Terrestrial Arthropod Reviews, 3, 111-128.

Ren, D., Labandeira, C.C., et al., (2009) A probable pollination mode before angiosperms: Eurasian long-proboscid scorpionflies. Science, 326, 840-847.

Shelomi, M. (2019). Entomoludology: Arthropods in Video Games. American Entomologist, 65, 97–106

Tong, X., Zhong, W. & Hua, B.Z. (2018) Copulatory mechanism and functional morphology of genitalia and anal horn of the scorpionfly Cerapanorpa dubia (Mecoptera: Panorpidae). Journal of Morphology, 279, 1532-1539.

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