September 2011 Notes 427 INFESTATION OF A NATURALLY INCUBATED NEST OF THE ALLIGATOR SNAPPING TURTLE (MACROCHELYS TEMMINCKII) BY THE PHORID FLY MEGASELIA SCALARIS SAMUEL R. HOLCOMB* AND JOHN L. CARR Department of Biology and Museum of Natural History, University of Louisiana at Monroe, Monroe, LA 71209-0520 Present Address of SRH: Louisiana Department of Wildlife and Fisheries, P.O. Box 98000, Baton Rouge, LA 70898-9000 *Correspondent: [email protected] ABSTRACT—Larvae of the phorid fly Megaselia scalaris were in eggs in a naturally incubated nest of an alligator snapping turtle (Macrochelys temminckii). It appears that these larvae contributed to failure of this nest. Infestation by phorid larvae has been reported previously for eggs and nests of multiple species of turtles, but has not been reported from M. temminckii. RESUMEN—Larvas del dı´ptero Megaselia scalaris (Phoridae) fueron encontradas en los huevos de un nido de incubacio´n natural de la tortuga caima´n (Macrochelys temminckii). Parece que las larvas contribuyeron al fracaso del nido. Infestacio´n de huevos y nidos de varias especies de tortugas con larvas de moscas (Phoridae) se ha reportado anteriormente, pero no en M. temminckii. Infestation of turtle nests by flies is a common and nondeveloping eggs (Acun˜a-Mese´n and phenomenon, with dipteran larvae reported Hanson, 1990). It has been suggested that larvae from nests or eggs of multiple species of turtles of M. scalaris feed primarily on dead or weakened (e.g., McGowan et al., 2001; Hall and Parmenter, hatchlings (Fowler, 1979) and that adult M. 2008). Two dipteran families commonly report- scalaris may be attracted to odors associated with ed in nests are Sacrophagidae and Phoridae. rotting nonviable turtle eggs (Acun˜a-Mese´n and Larvae of Phoridae have been reported in nests Hanson, 1990; Broderick and Hancock, 1997; or eggs of the green sea turtle (Chelonia mydas; Saumure et al., 2006). However, Moll and Legler Fowler, 1979; McGowan et al., 2001), hawksbill (1971) reported that adult M. scalaris entered sea turtle (Eretmochelys imbricata; Bjorndal et al., turtle eggs through tears made by pipping 1985), loggerhead sea turtle (Caretta caretta; hatchlings and oviposited on eyes and yolk sacs Broderick and Hancock, 1997; McGowan et al., of hatchlings, which subsequently died. 2001), eastern box turtle (Terrapene carolina; First-instar larvae of M. scalaris are small Ewing, 1933), Meso-American slider (Trachemys enough to enter rigid-shelled eggs through venusta; Moll and Legler, 1971), and painted pores in the eggshell (Acun˜a-Mese´n and wood turtle (Rhinoclemmys pulcherrima; Acun˜a- Hanson, 1990). There is no information about Mese´n and Hanson, 1990). the ability of such larvae to enter hard- The phorid most commonly identified from expansible eggs, such as those of alligator nests of turtles has been Megaselia scalaris,a snapping turtles (Macrochelys temminckii;Ewert, species in which the larvae feed on a broad 1979). Wolff (2007) reported that phorids will spectrum of decaying organic matter (Disney, deposit eggs on healthy chelonian eggs, so flies 2008). Megaselia scalaris is known as a scavenger, that initially are attracted to decaying eggs also facultative predator, parasitoid, and parasite may take advantage of normally developing (Disney, 2008), so it can be unclear whether eggs present in the nest. Some members of larvae of M. scalaris in nests of turtles are Phoridae are able to burrow #1 m into soil as scavengers or parasitoids (Broderick and Han- adults (Disney, 1994), which means that turtle cock, 1997). This already confusing situation is eggs potentially are vulnerable to infestation at further complicated by indications that M. any time during development (Broderick and scalaris is capable of attacking both developing Hancock, 1997). THE SOUTHWESTERN NATURALIST 56(3):427–429 428 The Southwestern Naturalist vol. 56, no. 3 Research on nesting ecology of M. temminckii developed hatchling, including bones, scutes, has been ongoing since 2002 at Black Bayou and nearly intact tail. The portion of the eggshell Lake National Wildlife Refuge, near Monroe, containing the two small holes was preserved in Ouachita Parish, Louisiana. Nesting by M. alcohol, along with some of the puparia. Similar temminckii at the refuge was concentrated pri- observations were made regarding four addition- marily along a railroad causeway, where nests al eggs. In addition, two eggs were as described suffered high levels of depredation by raccoons, above, but also had fly puparia on the outside of Procyon lotor (Woosley, 2005). To find nests the eggshell. Three other eggs had small holes, before they were destroyed, surveys were per- remains of hatchlings, and internal puparia, but formed daily during nesting season in April and the eggs were invaginated so that the egg had a May, and all intact or partially intact nests were bowl-shaped appearance. This could have been covered with a predator excluder. We found a the result of dehydration of the egg caused by total of 11 nests in 2008, three of which were feeding of larval flies (Acun˜a-Mese´n and Han- depredated by mammals before we found them; son, 1990). One egg had small holes and fly the other 8 were intact or partially intact. For all puparia, but no remains of a hatchling. This egg intact (n 5 5), and two partially intact nests, the presumably was infertile, or experienced early nest-cavity was carefully excavated and the clutch embryonic death, and was entirely consumed by was divided in two. One-half of the clutch was fly larvae. Three eggs had large tears in the returned carefully to the nest and reburied in a eggshell, such as would be caused by a pipping manner similar to arrangement of the original hatchling, as well as remains of hatchlings and fly nest, and the other one-half was taken back to puparia. The 15th egg was not recovered from the lab for incubation. Eggs left in the nest were the nest, although there were several pieces of covered with a predator excluder, which consist- eggshell from another egg. A total of 14 adult ed of a ca. 1-m square piece of 1.3-cm-mesh flies were recovered from inside five of the eggs hardware cloth staked to the ground, and were and the flies were identified as M. scalaris; six left to incubate naturally. Nests were monitored, voucher specimens were deposited in the Louisi- but left undisturbed until well after estimated ana State Arthropod Museum at Louisiana State date of hatching based upon hatching in the lab University (LSAM 0154233-0154238). and data from previous field seasons. Two nests It appears that phorid flies played a significant were lost during incubation to mammalian role in failure of this nest of M. temminckii.Thefact predators despite use of predator excluders, that no living M. scalaris was recovered, coupled which resulted in a total of five nests that were with the fact that empty puparia persist long after monitored through the end of incubation. the adult fly has emerged (Disney, 2008) would be The first nest in 2008 was found on 26 April consistent with infestation of this nest at pipping, and contained a clutch of 30 eggs. Of these, 15 as described by Moll and Legler (1971), and eggs were replaced in the nest and were not indicates that the flies had completed their life disturbed again until excavation of all nests of M. cycle long before the nest was excavated. Pipping temminckii in the field was undertaken on 5 in M. temminckii is asynchronous, so a plausible December. As of that date, there had been no scenario is one in which flies were attracted to the emergence of hatchlings from the nest and the first eggs that pipped, and then proceeded to lay nest did not fall victim to above-ground depre- eggs not only on the pipped hatchlings, but also dation. When the nest was excavated, eggs were on the remainder of the clutch. Thus, remaining placed into resealable plastic bags and returned eggs were infested with fly larvae, which killed to the lab where they were refrigerated until they embryonic turtles in situ, leaving behind only were dissected in an attempt to determine cause indigestible scutes, bones, and tails. This could of failure of the nest. When the first egg was explain why only a few eggs in this clutch appeared examined, two small holes were noted in the to have pipped, yet most eggs contained remains eggshell. These small holes were measured, of well-developed hatchlings that seem to have along with similar holes (an average of 1.3 been close to pipping, at ca. stage 25–26 (Yntema, holes/egg, n 5 17) in other eggs, and averaged 1968). A similar scenario was described for a 1.45 by 1.60 mm (n 5 8). On the inside of the sarcophagid fly by Bolton et al. (2008), who eggshell, many empty fly puparia were noted, as suggested that female flies may be attracted by well as remains of what appeared to be a fully olfactory cues associated with hatching. It seems September 2011 Notes 429 likely that the first-instar larvae of M. scalaris would nurga importuna (Walker) (Diptera: Sacrophagi- be able to enter intact eggs of M. temminckii.Eggs dae). Canadian Journal of Zoology 86:151–160. of the confamilial eastern snapping turtle (Chely- BRODERICK, A. C., AND E. G. HANCOCK. 1997. Insect dra serpentina) have the same type of eggshell infestation of Mediterranean marine turtle eggs. (Ewert, 1979) and are characterized by arrange- Herpetological Review 28:190–191. DISNEY, R. H. L. 1994. Scuttle flies: the Phoridae. ment of the mineral layer into groups of shell Chapman and Hall, London, United Kingdom.