Scorpionflies

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Photographed in situ [1]

Looking within the expansive tall grasses in the woodlands, many long-legged insects choose to rest on broader surfaces such as the leaves of wood nettle (Laportea canadensis). Crane flies and scorpionflies have been especially abundant in the last week or so, joining the flurries of midges in the understory air. Of the more strikingly-patterned flies, above is a crepuscular species, the spectacled crane fly (Limoniinae: Epiphragma solatrix)Not much is known about the ecology and life history of E. solatrix, though its larvae feed on moist decaying logs and fungal mycelia.

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Male scorpionfly (Panorpa speciosa). Focus stack of three images; photographed after pursuit [3]

A male scorpionfly (Panorpa speciosa) displays his ‘tail’ upwards, hot in pursuit of a female. Arching his modified abdominal segments, he separates the terminal clasp and releases sex pheremones. In many North American species, this is as elaborate as the pre-mating ritual gets, with males flying and crashing down on females directly to mate. In other Panorpa species, however, they exhibit more complex behaviors. Males may possess alternative strategies to entice females in courtship— offering a dead arthropod or a mass of salivary secretion as ‘nuptial gifts.’ If accepted, the female will consume the nutritious reward during copulation. Ancestrally, male pre-copulatory behaviors likely involved the presentation of prey, and the production of salivary masses secondarily arose to reduce the costs of physical disturbance from other competing males. Although the second strategy may be advantageous due to prolonged copulation times, salivary masses can only be produced when food availability is high. Under poor environmental conditions, males that monopolize food items have a substantially higher probability of obtaining a mate.


Following the description of these behaviors, the mating system of Panorpa scorpionflies was previously established as a resource-defense polygyny, with fluctuating resource availability influencing male reproductive tactics. However, studies have since demonstrated a correlation between male condition and nuptial gift content, the latter of which could serve as an honest signal of male quality to reproductive females. Indeed, multiple female matings are actually common in scorpionflies, and females are less likely to re-mate after copulations involving large and nutritious gifts (‘cryptic’ female choice). If females mate with multiple males, sperm contribution to offspring becomes relevant to male reproductive fitness; analyses have suggested that lifetime copulation duration is the principal factor determining paternity. Lastly, there is limited evidence for males preferentially mating with females that produce a larger number of eggs. Therefore, mechanisms exist in both females and males that lead to high variance in the reproductive success of both sexes, atypical of simply a resource-defense polygyny.

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Female scorpionfly (Panorpa speciosa). Focus stack of two images; photographed in situ [1]

Female scorpionflies (pictured above) are slightly larger than the males, but lack the extended stinger-like abdominal segments. Given how strange scorpionflies are morphologically, I thought they might be related to the Neuroptera/Megaloptera/Rhaphidioptera clade. But they are actually sister taxa to snow scorpionflies (Boreidae [= Neomecoptera]) & fleas (Siphonaptera). Snow scorpionflies are a small enigmatic group, exclusively inhabiting high-altitude habitats. They are long-legged, using their hind legs to spring forward much like fleas, and also flightless, either lacking wings (apterous) or having reduced wings (vestigial structures). Similar morphological adaptations to icy environments are present in snow flies (genus Chionea), which belong to the crane fly subfamily Limoniinae. Both snow flies and snow scorpionflies have the ability to ‘supercool,’ withstanding ambient temperatures 5 to 7 degrees below zero without their internal organs freezing.

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Insect phylogeny from Misof et al. 2014
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Another Mecopteran, a hangingfly (Bittacidae: Harpobittacus australis), NSW, Australia. Photographed in situ [1]

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