Blow Flies Spit to Attract Homies

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In hip hop culture, rapping is all in how rhymes are spit to attract a crowd. In blow fly culture, flies also spit to attract crowds. Generally, we wouldn’t think of spitting as attractive but, in a recent article published in Insect Science, my collegues and I explain how blow flies co-opt semiochemicals associated with feeding or “spit” as a resource indicator.  The spit is an “international fly language” attracting flies of the same species and closely related species to lay eggs together.

Blow flies lay eggs together in groups called aggregations on a dead animal carcass (see photo below). In order to find each other, like most insects, they have been thought to rely on pheromones. However, repeated attempts to extract a pheromone failed, invoking doubt whether a pheromone really exists.  Conceivably, the reproductive biology of blow flies may be linked to carrion resources. Simply by regurgitating and feeding on carrion, flies may enhance its attractiveness. These feeding flies may inadvertently attract gravid (flies with eggs) and non-gravid females and even males. Based on their sex, age and reproductive status, flies attracted to a resource may then obtain meal, find a mate, or lay eggs.

Egg-laying aggregation of blow flies, Lucilia sericata (Family: Calliphoridae) on rat carrion.  (Photo by Sean McCann)
Egg-laying aggregation of blow flies, Lucilia sericata (Family: Calliphoridae) on rat carrion. (Photo: Sean McCann)

If flies were to aggregate on a carrion resource in response to feeding flies rather than ovipositing flies, then the semiochemical cue(s) may be present in the vomitus or salivary secretions of flies. As early as 1955, Dethier noted that fed-on food was more attractive to blow flies than non-fed on food. Even if the flies do not signal themselves, their salivary secretions may contain enzymes and microorganisms that initiate the breakdown process of the carcass (Dethier, 1955; Telford et al., 2012).

Working with two species of blow fly, Lucilia sericata and Phormia regina, we show that female blow flies of varying reproductive stages present on an oviposition site enhance its attractiveness to fellow female blow flies.  We conclude that their is not an oviposition pheromone, but rather female flies co-opt semiochemicals associated with feeding flies of varying reproductive stages as resource indicators.

The digestive fluid, such as spit, is in addition to other strategies flies use to improve the resource and increase benefits of their offspring. House flies (Diptera: Muscidae), for example, preferentially lay eggs near freshly deposited eggs of their same species. The maggots warm and moisten the resource and prevent fungi from taking over. Similarly, aggregated oviposition by blow flies increases the fitness of their offspring because, with large numbers of maggots, relatively fewer are eaton by predators. Additionally, these maggots develop quickly by sharing digestive fluids and taking advantage of elevated temperatures.

So, it’s beneficial for flies to be “Rollin’ with their Homies”.  I’d spit you a rhyme if I could but, for the flies, it’s just simply all in the spit (not the rhyme)!

Read the full article:

Brodie, B.S., W.H.L. Wong, S. Vanlaerhoven, and G. Gries.  2014. Is aggregated oviposition by the blow flies Lucilia sericata and Phormia regina (Diptera: Calliphoridae) really pheromone-mediated? Insect Science. DOI: 10.1111/1744-7917.12160

Citations:

Dethier V.G. (1955) Mode of action of sugar-baited fly traps. Journal of Economic Entomology, 48, 235–239.

Telford, G., Brown, A.P., Rich, A., English, J.S.C. and Pritchard, D.I. (2012) Wound debridement potential of glycosidases of the wound-healing maggot, Lucilia sericata. Medical and Veterinary Entomology, 26, 291–299.

Blow flies spitting on rat carcass.
Blow flies “spitting” on animal carcass. (Photo: Sean McCann)

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