Effects of the moon on animals

Casual observations and unsubstantiated folklore
The scientific evidence
Tidal rhythms
Monthly rhythms

This page is still in its early stages. References which I have quoted in full on this page are ones I haven't managed to look up yet.

Some of this stuff is relevant to the page about Lunar gardening

Casual observations and unsubstantiated folklore

The Miskito Indians of Eastern Nicaragua, believe that all animals respond to the tide, that the woodpecker pecks when the tide is changing, and that hunting and fishing is best at the rising tide but not at new moon. They also believe that
crops should be planted and harvested at certain phases of the moon.

In a similar way, South sea islanders believe that whale sharks are most easily caught a few days after full moon. [5]

Another belief is that castrating and weaning of animals should be done at certain phases of the moon, or when the moon is in a certain sign of the zodiac. See the links below for more on this. [top]

The scientific evidence

Tidal rhythms

Numerous scientific papers have been written on tidal rhythms in marine animals.
Crabs and other crustaceans seem to feature in these studies quite a lot, probably because they are affected by the tides [2][3][10][11].

In these cases, the animals seem to be following two rhythms: a daily (24 hour) rhythm, and a tidal (24.8 hour) rhythm*. These rhythms persisted in the laboratory under conditions of constant light and temperature.

In many crustaceans, renewal of shells, sexual activity, and regeneration of lost limbs all follow lunar tidal rhythms (Nouvel, H. (1945) Bull. Inst. Oceanogr. Monaco, 42 878; Wheeler, J.F.G.J.Linn.Soc.Zool., 40 325). Activity of crabs has been measured, usually by placing the crabs in a tray, balanced on a knife edge, and connected to a rotating drum to record any movements which the crabs make.
Fiddler crabs often became more active at the times when their burrows would have been uncovered by the tide. [10].

Activity of the shore crab Carcinus maemas L. follows a lunar tidal rhythm (Naylor, E., Atkinson, R.J.A. and Williams, B.G. J.Interdiscipl.Cycle Res. 2 2: 173-180), as does the crab Sesarma [3]. Oxygen consumption in the Fiddler crab, Uca pugnax follows a daily rhythm and a tidal rhythm. ([2] ; Webb, H.M. (1971) J.Interdiscipl.Cycle Res. 2 191-198).

Tidal rhythms of activity have also been observed in fish, such as Blennius pholis [9]; amphipods [12]; Mussels (Rao, K.P. (1954) Biological Bulletin 106 357-9); algae [8]

In these examples, the animals may be responding to moonlight, gravity effects and possibly changes in temperature. In some cases the rhythm persists when they are kept in the laboratory under constant light and temperature, in other cases this is not so. Tidal rhythms may be modified daily rhythms, as in some cases the animals switch from a 24.8 hour tidal rhythm, to a 24 hour rhythm in the lab.

A study by Korringa (Vakblad Biol. Sept. 1947 129-137) apparently showed that oysters could respond to changes in the force of gravity associated with the tides. I vaguely remember reading about something like this in Supernature by Lyall Watson. Oysters were moved miles inland to Iowa or somewhere, and they began opening and closing their shells at the time that the tides would rise and fall, if there were tides in Iowa. I also read a sceptical article suggesting that this was simply due to a change to the circadian cycle, that often happens when animals are taken out of their natural environment

Fiddler crabs also change colour daily, becoming lighter at night and darker in the day. On top of this 24 hour rhythm is a 12.4 hour tidal rhythm, which relates to the time at which their burrows are uncovered by the tide. The two rhythms coincide every 14.8 days, producing a noticable semi-monthly colour change. This could be relevant to the next section:

Monthly rhythms

The phase of the moon seems to influence the behaviour of a number of animals. In many cases, the animals are simply responding to the changes in light, which may (for example) make them more visible to each other or to predators, but it is possible that there are monthly circadian rhythms in operation (as in humans), or that the animals are responding to gravitional effects. As in the case of
The moon's effects on plants, I am a bit sceptical of the latter hypothesis.

The Palolo worm, Eunice viridis is found on several coral islands in the South Pacific, especially near to Samoa and the Fidji Islands. The palolos reproduce by swarming during the last quarter of the moon in October and November. The terminal parts of their bodies drop off and float over the surface of the water, releasing sperm and eggs. This event is/was so important to the inhabitants of the Banks Islands, that it featured in their Lunar Calendar.
A similar species is found in the Atlantic, but here swarming takes place in June or July during the first quarter of the moon. [1]

I have it on good authority that spiny lobsters in the red sea avoid foraging at full moon because of the threat from sharks.

Clunio marinus has reproductive cycles synchronised with the phases of the moon (Caspars, H. (1951) Arch.Hydrobiol 416-594)

The breeding behaviour of the Malayan Black Rice Bug seems to be synchronised with the phases of the moon. More young males rice bugs are caught in light traps at full moon than at any other time. Black rice bugs are serious pests of rice in the far-east [7]. I suppose this may be similar to the behaviour of moths which fly into lights: They navigate by the light of the full moon, so when they encounter other bright lights, they fly around them in circles.

Gerbils in the Negev desert forage more for seeds at new moon than at full, because at full moon they are far more likely to be caught by owls [6].

The moon seems to affect trout fishing. Between 1959 and 1968, the largest catches of trout in lake Neuchatel in Switzerland were just before or just after new moon, and the smallest catches were during full moon (Quartier, A.A.(1970) Influence de la lune sur la peche des truits du lac de Neuchatel. Rapport de la Bibliotheques et des musees de la ville de neuchatel).


*12.4 hours is the time between two successive high or low tides. 24.8 hours is a "lunar day". Tides are greatest at new moon, when the gravitational pull of the sun and moon are both acting in the same direction. Because the moon is moving relative to the earth and the sun, the "lunar day" is not precisely 24 hours.[back]

Links to other sites on the web

Dreamaker Farms
Dreamaker Farms breed Black/White Tobianos and Buckskin Missouri Fox Trotting Horses. Foals are weaned and castrated according to the phase and sign of the moon.
The old farmers almanac
Contains information on castrating and weaning animals by the phase of the moon
Castrating, moon phases and signs

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