Porcellio Scaber Behavior

It has been studied that Isopods are very active when it comes to varying conditions in their environment. This activity leads them to be typically found in dark, moist, and crowded places. Isopods are known by several names: sow bugs, pill bugs, or woodlice. Because of the large number of species in the isopod order, it was necessary to determine the specific family of which the studies were done. Pill bugs are classified in the family Armadillidae and can roll themselves into a small ball. However, the animal being studied here was unable to perform this activity and was determined to be a sow bug species. More specifically, this species is a member of the Porcellionidae family. The Porcellios are a group of animals that are grayish in color and when it is disturbed it tends to quickly run away. The head is crown shaped with the two outer lobes being rounded. It has two pairs of projections on the rear of the body called uropods. The inner pair of uropods is much smaller than the outer pair. The posterior ends of the plates of the exoskeleton tend to come to a sharp point. On the underside of the body there are two pairs of pleopod lungs. The outer margins of the plates of the exoskeleton are slightly reverse curved in the upward direction. They have 7 pairs of legs and their bodies consist of three fused sections so that it is difficult to be sure where each section starts or finishes.

Woodlice, as they are also referred, are often found in the upper layers of compost heaps, under rotting wood or logs, under surfaces or stones, and in other dark, damp places. Woodlice belong to the biological class Crustacea. Most of the animals in this class are aquatic, and although the terrestrial species can breath with the aid of primitive "lungs," they lack the features found in most other land dwelling arthropods. They do not have a waterproof waxy cuticle on their exoskeleton, like insects, and are therefore more likely to suffer from desiccation compared with other arthropods, which have a well-developed waxy layer. These animals excrete their nitrogenous waste as ammonia gas directly through their exoskeleton, which means that their exoskeleton needs to be permeable to ammonia and is therefore also permeable to water vapor. Most other animals excrete their nitrogenous waste in the form of urea or uric acid, so woodlice do not have to expend energy on such processes. The fact that woodlice prefer high humidity and cooler temperatures is a direct response of the permeability of their exoskeleton to water and the loss of water from their bodies. These preferences are behavioral adaptations to help reduce desiccation. The experiments preformed here are testing this theory and demonstrating this behavior.

Many of the behavioral responses of woodlice are concerned with water conservation and the need to avoid desiccation. They have a relatively high surface area to volume ratio and are therefore likely to loose water by diffusion more quickly than many other species. Porcellio scaber show a kinesis type response to moisture. They show both an increased speed of movement, or orthokinesis, and increased rate of turning, or klinokinesis, in dry conditions and slower rates of movement in more damp conditions. This response will result in them accumulating in more damp regions, and so will not loose water from their bodies. Interestingly, it has been reported that woodlice taken from very damp conditions show a different reaction. They may either show no difference in their reaction to changes in moisture or may even actively avoid the damp regions in preference for the drier regions (Sutton, Woodlice, 1972). Woodlice also show a positive orthokinesis as the temperature increases or decreases from their preferred range. Their rate of turning also seems to show a similar response. By moving more rapidly, they are likely to spend less time in these unfavorable conditions and therefore will avoid unnecessary desiccation. They are known to show a negative phototaxis as well. This would result in them moving away from bright conditions towards darker regions. Brighter conditions tend to be drier and warmer than dark conditions, so this behavior will again result in decreased desiccation. Finally, these animals have been shown to demonstrate positive thigmokinesis. This means they are less active when more of their body surface is in contact with other objects, including other woodlice. They will move around so that the maximum amount of their body is in contact with other objects. This behavior results in woodlice forming groups or clumps and also means they will tend to congregate in cracks and crevices. In any case, they will have better protection from desiccation and also predators.

In order to demonstrate the effects of temperature and moisture on the animals, a chamber was set up with an underlying grid, used for calculations. The chamber could be altered in order to create a different environment. In this case, temperature was varied from cold, to room temperature, to warm. In each temperature range, damp versus dry was compared. The animal was placed in the chamber for a period of time and recorded using a digital camera. Upon playback of the video, the number of squares the animal covered over the period of time was calculated to give a value of orthokinesis. Also, the number of turns made by the animal was counted to demonstrate the value of klinokinesis occurring in each environment. These values were then tabulated and compared.

Cold-Dry				Cold-Wet
Run	Squares Covered	Time	Orthokinetic Value	Run	Squares Covered	Time	Orthokinetic Value
1	122	300	0.4067	1	9	180	0.0500
2	206	300	0.6867	2	41	180	0.2278
3	62	180	0.3444	3	34	180	0.1889
4	42	180	0.2333	4	59	300	0.1967
5	97	180	0.5389	5	72	300	0.2400
6	76	180	0.4222	6	18	180	0.1000
Average =	0.4387			Average =	0.1672

Room Temperature-Dry				Room Temperature-Wet
Run	Squares Covered	Time	Orthokinetic Value	Run	Squares Covered	Time	Orthokinetic Value
1	129	300	0.4300	1	2	300	0.0067
2	149	300	0.4967	2	34	300	0.1133
3	73	180	0.4056	3	37	180	0.2056
4	96	180	0.5333	4	21	180	0.1167
5	262	180	1.4556	5	24	180	0.1333
6	104	180	0.5778	6	13	180	0.0722
Average =	0.6498			Average =	0.1080

Warm-Dry				Warm-Wet
Run	Squares Covered	Time	Orthokinetic Value	Run	Squares Covered	Time	Orthokinetic Value
1	103	94	1.0957	1	16	31	0.5161
2	38	31	1.2258	2	11	30	0.3667
Average =	1.1608			Average =	0.4414

Cold-Dry				Cold-Wet
Run	Turns	Time	Klinokinetic Value	Run	Turns	Time	Klinokinetic Value
1	3	60	0.0500	1	2	60	0.0333
2	15	60	0.2500	2	9	60	0.1500
3	16	60	0.2667	3	11	60	0.1833
4	6	60	0.1000	4	8	60	0.1333
5	8	60	0.1333	5	11	60	0.1833
6	2	60	0.0333	6	7	60	0.1167
Average =	0.1389			Average =	0.1333

Room Temperature-Dry				Room Temperature-Wet
Run	Turns	Time	Klinokinetic Value	Run	Turns	Time	Klinokinetic Value
1	16	60	0.2667	1	2	60	0.0333
2	33	60	0.5500	2	4	60	0.0667
3	22	60	0.3667	3	16	60	0.2667
4	18	60	0.3000	4	21	60	0.3500
5	31	60	0.5167	5	11	60	0.1833
6	14	60	0.2333	6	17	60	0.2833
Average =	0.3722			Average =	0.1972

Warm-Dry				Warm-Wet
Run	Turns	Time	Klinokinetic Value	Run	Turns	Time	Klinokinetic Value
1	57	60	0.9500	1	9	31	0.2903
2	41	31	1.3226	2	7	30	0.2333
Average =	1.1363			Average =	0.2618

Both experiments followed the predicted outcomes. The orthokinetic experiment showed that the rate of movement increased with temperature. The discrepancy in the moist environment is most likely due to the animal pausing at moist points to take up water. This is seen in the cold and room temperature environments. The warm environment was highly unfavorable for the animal in any case. This is due to the heat causing excessive desiccation.

In the klinokinetic experiment, the same predicted outcomes were observed. The rate of turning increased with temperature. One result to point out here is that the rate of turning increased much more in the dry environment than in the wet environment. This would most likely be due to the fact that a wet environment is favorable over dry for the animal, so it is to be expected that the rates are higher for the dry environment.

One behavior that was noticed during the experiment was the use of the uropod structures at the posterior of the animal. Woodlice get water with their food, but they can also drink it through their mouth and also by using their uropods. The uropods are tube-like structures on the posterior of the animal. When they use them for drinking they press their uropods close together and touch it against a moist surface. Capillary action pulls the water up the uropods and into the anus. The above picture shows the uropod lifted in order to prevent suction of water.

Woodlice, along with most other crustaceans, have the compound haemocyanin in their blood. Haemocycanin carries oxygen in the same way that hemoglobin does in mammals. Haemocycanin contains a copper atom instead of the iron atom found in hemoglobin. The blood is pale blue when it is carrying oxygen and colorless when it is not carrying oxygen. Because a woodlouse contains very small amounts of haemocycanin, it is not possible to see these color changes by direct observation. There are cases of blue woodlice. An iridovirus can infect woodlice and at advanced stages of infection virus accumulates in such large numbers that it forms crystalline structures in the diseased tissues. These crystalline structures give an intense blue or purple color to the woodlice. Individuals infected to this extent will usually die within a short time.

Another interesting fact about woodlice is that they have the ability to change sex. Male woodlice infected by Wolbachia bacteria will turn into female woodlice. The bacteria upset the normal action of the male hormone. Bacteria are passed to the next generation in the cytoplasm of the egg cells, and this process means that there is a better chance of Wolbachia survival as all infected offspring will be female and therefore will all allow infection of the third generation of woodlice.