What causes bubbling in hermit crabs?

I wrote to an expert on Crustacea and Decopodae, who has also done some biological work with respect to land lermit crabs. I am reporting what he told me. Something to note though, he does not provide a definitive tolerance level regarding temperature. But note, relative humidity is temperature dependent...meaning that in order for your humidity to be higher, so must your temperature be higher.

This is for dehydration:

Most crabs bubble brown fluid when stressed and rough handling is often enough to provoke it. (rough handing is classified as arid conditions below 65% RH, temperatures exceeding 33C {92F}, where no cover is present)

The brown fluid is regurgitated from the fore gut and bubbles in the exhalant respiratory air streams, which exit close to the mouth. The fluid contains surfactants (A substance composed of lipoprotein that is secreted by the alveolar cells of the lung and serves to maintain the stability of pulmonary tissue by reducing the surface tension of fluids that coat the lung.) which cause the bubbling. This effort does further damage the gills and they will die up to 3 days from the time they do.

This is pertaining to OVER saturation (there is more than one process, as the crabs have a couple of ways to control their temperature:

Coenobita carry fluid in the spiral part of the shell (generally clear and colourless) and this can be used for evaporative cooling of the body at high temperatures. The osmotic pressure of the fluid is regulated by the animal by selective drinking of water of different osmotic concentrations (in our tanks that is regular water and ocean salt water...which they use more for cooling). If the fluid available for drinking and adding to the shell is more dilute (not enough salt) than preferred, the crabs will enhance evaporation from it to make it more concentrated and may hang out of the shell to achieve this. If the humidity is too high, they will not be able to achieve this, and will overheat. This results in them leaving their shell. For details of these mechanisms you need to read de Wilde 1973 or the summary in my chapter in Biology of the land crabs 1988 (copy attached) - references are given in my 2003 paper. Your crabs at 90% RH may be trying to increase evaporation either to cool or may be trying to concentrate shell water or cool themselves what temperature were they at? In Celsius the temp ranges you are using will be ~22-28C. (72-84F) I would think these should be in the acceptable range.

So what this means is that temps over 84 and humidity over 85% can only be tolerated in a closed environment for a short time. While some will be able to burrow in a cooler area of a tank, it is important that there is a temperature range! The accepted ranges ARE: 72 - 84 degrees for temperature...the RH (relative humidity) ranges are from 72 - 82%

Hopes this explains a little clearer why this occurs!

Sue/Chestersmom