Caliherp,
Your comments have encouraged me to share more of what I know with you and to chase up a few figures I have long been intending to....
On this topic, which is something I have been interested for many years, I have always found it is particularly difficult to procure information on the effects of mites on lizards, in particular on geckos. The following is based upon my own observations and is yet to be properly verified by a scientific report that I can locate. I believe that many mites affecting geckos and agamids are parasitic and not simply commensal. They tend to be located where the skin is thinnest – the armpits, the ears and around the eyes. This, to me, indicates they are likely to be drawing blood or body fluids from the host. However, those species found more widely distributed on the body of an animal may well be living on the outer layer of skin, as do the common dust mite found in human habitation. These mite possess the gut structure to break down the difficult to deal with compounds that skin is composed of – rather like the stomachs of ruminants and their ability to break cellulose. I am uncertain as to how many species are red or orange or yellow and as to the potential degree of colour variation in any given species.
My apologies that this generates the usual scenario – more questions than answers. I have known for some time, based on reliable sources, that there are around 3,000 mite species in Australia. I recently managed to locate a figure for the actual number of species that have been described, compliments of one Dr. Bruce Halliday, a CSIRO expert on Acarina - 2620 described species of mites that are known to occur in Australia. At the same time, compliments of Karingal Vet Hospital, we have the statement that there are over 250 different species of mites that have been reported to parasitise reptiles. If you are interested, the two main groups known to infest lizards are trombiculids and pterygosomatids.
A particular study found that Shinglebacks with the most severe tick infestations appear to achieve the largest mature size and mate more than those animals with minimal infestations. Weird, hey? I wonder if we can say the same for geckos and mites? All I can say from observations is that mite load on geckos does not appear to affect their abilities of movement or response.
Blue