132 
Psyche 
[September 
Table 1. Acridiids 
weighted and unweighted, 
lengthened 
and normal. 
Behaviors. 
Prey A 
Prey B 
Prey C 
1. Bite and back off. 
yes 
4 
1 
1 
no 
6 
9 
9 
2. Bite, legs raised. 
yes 
9 
4 
2 
no 
1 
6 
8 
3. Wrap in web. 
yes 
7 
7 
2 
no 
3 
3 
8 
Ten spiders chosen at random from wild population receive A, ten 
captive spiders B ten wild spiders C. A is acridiid with weight added 
and lengthened (total weight ca. 1000 mg length 70 mm). B is acridiid 
lengthened to 70 mm weight 400-550 mg. C is unmodified length 25-30 mm 
weight 400-550 mg. 
Statistical analysis — Fisher’s exact probability: differences between A 
& B, A & C, B & C for Bite and back off are not significant; difference 
between A & B significance level 0.05, difference between A & C significance 
level 0.005, no signficant difference between B & C, all for Bite, legs raised; 
for wrap in web difference between A & B and B & C level of significance 
0.05. 
All levels one-tailed 
Although this number is not statistically significant we regarded the 
occurrence of this behavior in attacks on the weighted insects as 
being highly suggestive. We then carried out a further series of 
experiments, using similar sized acridiids, in which we quadrupled 
their weight. 
We found that very heavy dummies of small size often dropped 
out of the webs before the spider reached them. We therefore in- 
creased the length of both experimental (very heavy) dummies and 
controls (normal weight) by adding the toothpick to the insect. 
This worked in a perfectly satisfactory way to distribute the weight 
over a greater number of web members. As before, we vibrated 
the dummies until the spider commenced its predatory excursion. 
The results are given in Table 2. There is a statistically significant 
effect of weight on the occurrence of the bite & back-off attack 
behavior. Note that we did not induce this attack behavior in all 
the presentations; we consider that with large, heavy active insects 
there may be some heterogeneous summation. We attempted to test 
for the possible additive effect of activity, at the moment of contact 
