The Increasing Parasitism of Flesh Flies on Green Anoles

Growing up in Louisiana, always fascinated with reptiles and insects, my first reptilian love was the green anole (Anolis carolinensis). They're abundant in the south, but less so in recent years. 

There are many factors that are contributing to the favorite friendly lizards of many Louisiana residents. One of them is the appearance of a fierce and competitive relative, the brown anole.

The green anole, Anolis carolinensis (bottom),
compared to a brown anole (Anolis sagrei). [Picture from UOF]

Another issue I've noticed an uptick in during recent years, especially as the weather grows colder, is the Sarcophagid fly infestations. Based on my cursory research of the topic on forums for reptiles and specifically anoles, the bulk of the reports come from 2015 or later. However, a study (Effects of Sarcophagid Fly Infestations on Green Anole Lizards) from Tulane University states, 

"Sampling by age and sex classes during two years (2003 and 2004) revealed that adult male anoles were infected at an unusually high rate (up to 16%) compared to other populations (only a few documented cases over the past 60 years)..." 

Personally, I've seen three cases within the past three years, but none before that in the peak of my green anole obsession. This further leads me to believe this issue is becoming only more prevalent. 

The green anole population is by no means in a critical decline, but these hilarious and inquisitive backyard friends are unfortunately becoming less likely to be found on your porch these days. Let's take a look at the infestations that may be contributing to their dropping numbers.

The Sarcophagid Fly

[Image from KZN Department of Health]

Sarcophagid flies, also known as flesh flies, have an interesting distinction from other families. They're ovoviviparous, meaning that the fertile eggs of females hatch inside them and the first instar maggots are deposited on decaying corpses, waste material, or open wounds. This unusual method of procreation spells a big problem for vulnerable green anoles, which are being found bearing the wounds of the larvae or large, writhing nodules on their sides. 

Interestingly, because of their opportunistic feeding habits and their typically speedy arrival to fresh dead meat, they are common among forensic entomologists. They can play a surprising role in criminal analysis, as well as their larvae's aid in breaking down organic detritus.

Larval Effects on Anoles

So how does a flesh fly infection impact the anoles? That question's answer depends on how many larvae inhabit the host and how far in their life cycle the flies are. One such case reported by Claudia S. Copeland contained as many as nineteen larvae inside of a single adult! 

Anoles hosting the Sarcophagidae larvae often display physical signs of the infection. One such sign is the aforementioned nodules protruding beneath the surface, usually near a leg or the original wound. There may be necrotic or scarred tissue where the larvae originally entered as well. When the lizard is infected, depending on the progression and growth stage of the flies, they may become lethargic or paralyzed in the limb closest to the wound. Movement in the side of the body the flies are currently congregating in may be stuttered, slow, or seem hindered in some way. 

The entry hole in a male of a similar
species, Anolis krugi [Source: Chipojo Lab]

A curious freshwater fish ecologist who was conducting a research study on the breeding of Anolis krugi, Travis Ingram, converged with several other ecologists on his blog about the parasites. Other relevant research suggested that it's primarily the males that suffer from the infection of the larvae, and especially those who live in higher humidity levels. There is not enough knowledge yet on why exactly these lizards are seeing higher rates of infestation, but there is speculation that it has to do with an increase in the fly population or a decrease in the anoles' resistance to them. 

With any hope, nature will right itself and balance out the ecosystem in the lizards' favor, that way we can step outside and see anoles o'plenty again. In the meantime, some people are finding luck in gently trying to coax the larvae out if there is an open wound visible, or using tweezers to pull out the parasites manually. One commenter on Ingram's blog even said she was able to surgically remove the larvae and the lizard made a full recovery!