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Genus Vermileo

Los Angeles wormlion - Vermileo opacus Los Angeles wormlion - Vermileo opacus Sierra wormlion - Vermileo comstocki wormlion - Vermileo comstocki Sierra Wormlion - Vermileo comstocki Vermileo image w/ palps indicated by arrows - Vermileo comstocki - male wormlion - Vermileo opacus - female Vermileo larva from a new station - Vermileo comstocki
Classification
Kingdom Animalia (Animals)
Phylum Arthropoda (Arthropods)
Subphylum Hexapoda (Hexapods)
Class Insecta (Insects)
Order Diptera (Flies)
No Taxon (Orthorrhapha)
Infraorder Tabanomorpha
Family Vermileonidae (Wormlions)
Genus Vermileo
Numbers
2 spp. in our area. Around 11 spp. worldwide (depending on circumscriptions): 6 from the New World [see Pechuman(1938) and DeLeon(1938)]; 4 from the mediterranean area; and 1 from Sudan.
  Vermileo opacus (Coquillett), 1904   [Orig. Description as Pheneus opacus in Baker(1904)]
  Vermileo comstocki Wheeler, 1918   [Orig. Description]
Range
V. comstocki: CA
V. opacus: CA, CO, NV, NM, ID, UT  
Food
Larvae take prey that fall into their sand traps, most commonly ants (see video here).
Adults feed on nectar...typically from open flowers (due to their short proboscis).
Life Cycle
Adult females deposit eggs singly or in clusters beneath the surface of sand. Incubation requires about 1 week.
Larvae are worm-like...anteriorly, the body is tapered to a very small conical head capsule; posteriorly, it's distinctly enlarged towards the terminal end.
      larvae                  
The dorsum of the next-to-last abdominal segment has a comb-like row of spines along its posterior margin (used to anchor the larva in its burrow); and the last abdominal segment terminates in 4 large, conical tubercles (or "teeth"). There is also a single ventral pseudo-proleg on 1st abdominal segment, which is used to help grasp prey.
The newly hatched larva constructs a pitfall trap by shallowly burrowing beneath the substrate, and then throwing sand upward and outward with its head-end. The trap building process is illustrated in Figs. A & B here. Favored locations for traps include areas under rocks ledges or trees that balance requirements such as: appropriate sand depth, particle size & density; prey availability & abundance; shelter from rain and other disturbances; as well as micro-climate factors like shade, photo-period, soil temperature & soil moisture.
Devetak(2008), Eiseman & Charney(1)(2010), and Devetak & Arnett(2015) all note that — compared to the coarser-particle sand substrates used by antlions for their pitfall traps — those of wormlions usually occur in finer-dust (though some coarser-grains usually litter the surface surrounding wormlion pits). Moreover, wormlion pits usually occur in higher-density clusters of 6-9 or more (since wormlion eggs are laid in larger clutches) and often nearby pits occur with a variety of diameters (e.g. from 4-16 mm wide)...whereas antlion pits are usually larger & more uniform in diameter, and less numerous in a given patch. Also, the pitfall traps of antlions are typically more conical in shape (perhaps due to the coarser grains inducing a more uniform angle of repose), while those of wormlions are usually steeper-sided and broader at the bottom (though these distinctions can be subtle):
      wormlions         antlions
The wormlion larva lies on its back below the bottom of the trap waiting to capture prey that pass by and fall in, most commonly ants. The prey is then seized and drawn down into the sand, where the softer parts are consumed (video). The empty cadaver is then thrown from the pit by the larva.
Maturation of the larva is thought to normally require about a year (but is observed to be biennial or even triennial for Old World species). Pupation occurs in the sand and takes approximately a month. Adult Vermileo feed on nectar and typically live from 2 to 5 days (or more).
[Sketch above based on MND(2), Devetak(2008b), Eiseman & Charney(1)(2010), Devetak & Arnett(2015) and personal communication with Old World Vermileo researcher Dr. Christian Kehlmaier. (A.S. 8/31/17)]
Remarks
Vermileo is only genus in our area representing the family Vermileonidae, which is unique among Diptera in having larvae that capture prey by constructing pitfall traps in loose soil (like antlions in the order Neuroptera).
The family Vermileonidae is also interesting in terms its enigmatic place within the evolutionary and systematic context of the suborder Brachycera of Diptera. Traditionally placed as a subfamily of Rhagionidae, the group was given the rank of family of uncertain placement (incertae sedis) by Nagatomi(1977). Male terminalia in Vermileonidae resemble those of Therevidae in the superfamily Asiloidea, while larval mouthparts are similar to those of the superfamily Empidoidea.(2)
Vermileonidae has been variously placed as sister to Rhagionidae, or as its own infraorder sister to Xylophagomorpha near the base of Brachycera. It is apparently an old group...with the most recent work suggesting it is the most primitive family of the infraorder Tabanomorpha.
Print References
Baker, C. F. (1904). Diptera. Reports on Californian and Nevadan Diptera, I. Invertebrata Pacifica. 1:17-39 (Full Text)
DeLeon, Donald (1938) Notes on the Distribution of Vermileo in the United States and Mexico with a Description of a New Species. (Diptera: Rhagionidae). Ent. News 49:167-171 (Full Text)
Devetak, Dusan (2008a). Substrate particle size-preference of wormlion Vermileo vermileo (Diptera: Vermileonidae) larvae and their interaction with antlions. Eur. J. Entomol. 105:631–635. (Full Text)
Devetak, Dusan (2008b). Wormlion Vermileo vermileo (Diptera: Vermileonidae) in Slovenia and Croatia. Annales Ser. hist. nat. 18(2): 283-286. (Full Text)
Devetak, Dusan & A. E. Arnett (2015). Preference of antlion and wormlion larvae (Neuroptera: Myrmeleontidae; Diptera: Vermileonidae) for substrates according to substrate particle sizes. Eur. J. Entomol. 112(3):500–509. (Full Text)
Dor, R., S. Rosenstein & I. Sharf (2014). Foraging behaviour of a neglected pit-building predator: The wormlion. Animal Behaviour 93:69–76 (Full Text)
Leonard, M. D. (1930). A revision of the dipterous family Rhagionidae (Leptidae) in the United States and Canada. Mem. Am. ent. Soc. 7:1-81 (Full Text...Vermileo treatment here)
Nagatomi, Akira (1977). Classification of the lower Brachycera (Diptera). Journal of Natural History 11(3):321-335
Nagatomi, A., T. Saigusa, H. Nagatomi, L. Lyneborg. (1991). The systematic position of the Apsilocephalidae, Rhagionempididae, Protempididae, Hilarimorphidae, Vermileonidae and some genera of Bombyliidae (Insecta, Diptera). Zool. Science 8:593-607. (Full Text)
Ovtshinnikova, O.G. (2000). Male genital musculature of Vermileonidae (Diptera, Brachycera) and systematic position of the family. Entolmologicheskoe Obozrenie 79: 513-52l.
Pechuman, L. L. (1938). A synopsis of the New World species of Vermileo (Diptera-Rhagionidae). Bull. Brooklyn ent. Soc. 33: 84-89. (Full Text)
Petersen, Wade H., and Charles W. Baker. (2006). First record of wormlions (Diptera: Vermileonidae) in Idaho. Journal of the Idaho Academy of Science, 42(1).
Wheeler, William Morton (1918). Vermileo comstocki, sp. nov., an interesting Leptid fly from California. Proc. New Eng. Zool. Club 6:83-84. (Full Text)
Wheeler, William Morton (1930). Demons of the Dust. New York: W. W. Norton & Company, 1930.
Yeates, D.K. (2002). Relationships of extant lower Brachycera (Diptera): a quantitative synthesis of morphological characters. Zoologica Scripta 31: 105-121 (Full Text...scroll down page)
Internet References
The first half of this article, from the University of California Riverside, has interesting life history information on Vermileo.
See here and here for photos of adult Vermileo species from Portugal, and here for photos of adults and larvae of Vermileo vermileo (France).
Works Cited
1.Tracks & Sign of Insects and Other Invertebrates
Charley Eiseman & Noah Charney. 2010. Stackpole Books.
2.Manual of Nearctic Diptera Volume 1
Varies for each chapter; edited by J.F. McAlpine, B.V. Petersen, G.E. Shewell, H.J. Teskey, J.R. Vockeroth, D.M. Wood. 1981. Research Branch Agriculture Canada.