biology zoology blog benno meyer rochow jamaican cave flies

Jamaican Cave Flies

Jamaican cave flies got rhythm!

Is it surprising that I hope the Jamaican sprinter Usain Bolt will hold his world records over 100 and 200 m for many years to come? Is it surprising I have a soft spot for Jamaica? I suppose not, because two of my daughters were born there. But Jamaica is not just Usain Bolt: Jamaica is famous for rum, reggae and rhythm (and bauxite, but we’ll ignore that for now).

It’s a country full of life and certainly not a place you want to be sick: you’d miss out on all the fun this Caribbean holiday island has to offer. Well, I was sick once in Jamaica and meant to recuperate in a dark hospital room with drawn curtains. I felt a bit like a cave animal, cut off from the outside, accommodated in sparse surroundings with limited space, constant temperature, stale air, and poor and irregular food supplies. Most of the time I did not know what time it was, but I began to notice regularly and daily recurring signs like the smell of grilled meat wafting into my room at around mid-day or the starting of car-engines in the evening.

I was reminded of my research on the abundance and distribution of flies in Jamaican caves with Dr. Ian Stringer. One result of that work had been that flies of the family Scatopsidae occurred in the furthest and totally lightless regions of the caves. Yet, even there our hourly-monitored traps half a metre above the bat guano on the ground had revealed a clear difference in the number of flies active throughout the day; at night there were always far fewer of them in our traps, indicative of a dip in their activity. How come? They were so tiny; they could not possibly fly in and out the cave and look if it was day or night. They could only buzz around in total darkness for maximally a few metres and, besides, had very small eyes and would be mainly interested in the bat guano, their source of food and breeding ground. How could these little flies “time” their periods of rest and activity if none of the signals available to them existed inside the cave to determine it was daytime outside the cave? The cave’s interior was constantly dark and temperature oscillations between day and night were non-existent (we used high quality measuring devices). Other possible natural signals like barometric pressure, winds and drafts, or humidity fluctuations were equally useless as indicators of time inside the cave. And yet, our flies had a synchronized rhythm, no doubt about that.

We concluded that the flies were using the bats that were residing in the cave as a secondary clue for the non-visible external changes in brightness and we further suggested that the flying flies could themselves trigger or entrain fly-catching cave-spiders to coordinate their activities with the flies’ activity to optimize their catches. To our surprise, nobody before us seemed to have come up with the idea of secondary and tertiary time signals for obligate cave arthropods; these animals had hitherto been thought to be all without daily rhythms. Flying in and out of the cave during their nightly foraging trips and creating disturbances in the air, bats must have provided the flies with the signal to “duck” and get out of the way. And this happened every night and always at the same time. However, during the day the air inside the cave remained undisturbed as the bats were resting and digesting. This then was the period that signified to the cave flies “safety” and “food”, thus leading to the heightened day activity of members of the cave fly camp. Obviously, the sense of rhythm in Jamaica cascades down to even the smallest inhabitants of the island and just like I in my dark hospital room knew evening was approaching when car engines were revving up, our cave flies knew it was time for a rest when the bats were preparing to alight.

© Dr V.B. Meyer-Rochow and, 2019.
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