Figure 1.
Carton Azteca andreae nest and group ambush technique.
(A) A carton nest on a Cecropia obtusa. (B) Underside of a young C. obtusa leaf with numerous ambushing A. andreae workers placed side-by-side along the leaf margin. A black hymenoptera is spread-eagled near the principal vein. (C) A sphingid moth was captured during the night and was still struggling when we photographed it in the morning. (D) Detail of the position of ambushing workers.
Figure 2.
Illustration of the techniques used.
(A) To evaluate the number of Azteca andreae workers per centimeter of leaf margin, we took pictures of the workers ambushing from beneath the Cecropia obtusa leaves while cautiously placing a ruler 1–2 cm away from the leaf margin so as not to perturb them. (B) To evaluate the strength of the workers, we used different weights glued to pieces of thread and placed the free end of the thread near an ambushing major worker. Here, three Azteca andreae workers are biting the end of a piece of thread glued to a 10-cent Euro coin; only one (arrow) is really holding onto the coin (4.11 g).
Table 1.
Different captured prey, their weight (or mean weight ± SE) and the ratio with the mean weight of a hunting worker (ca. 0.0014 g).
Figure 3.
Percentages of cases when hunting Azteca andreae workers are able to hold onto different weights.
(A) From the upper side and the underside of C. obtusa leaves, and from a sheet of supple plastic (Kruskal-Wallis test for 0.75 g: H3,300 = 12.4; P = 0.002; for 0.125 g and 0.250 g: H3,300 = 74; P<0.0001; Dunn's post hoc test for multiple comparisons: different letters indicate significant differences at P<0.01). (B) From the underside of C. obtusa vs. C. palmata leaves (Wilcoxon signed rank test: Z = 2.37; P<0.02).
Figure 4.
The hook-and-loop system permitting Azteca andreae workers to catch large prey.
(A) Scanning electron micrograph of the hook-shaped claws of A. andreae workers. (B-C) Photomicrographs of unstained, 50 µm sections of Cecropia obtusa (B) and C. palmata (C); the upper side of the lamina is on the top. D-G- Scanning electron micrographs of the upper side (D–E) and underside (F–G) of the lamina of C. obtusa (D–F) and C. palmata (E–G). Long, thin trichomes characterize the underside of the leaves of both species, but with major differences in densities; whereas the upper surface of the leaves has short, wide trichomes – here, too, at different densities. Scale bars, 100 µm.
Figure 5.
Capture of locust nymphs from four size classes on Cecropia obtusa, C. palmata and Vismia latifolia.
The tests consisted in dropping 1 cm, 1.5 cm, 2.5 cm and 3.5-cm-long nymphs of the locust species Tropidacris collaris onto the upper surface of C. obtusa, C. palmata or V. latifolia leaves where groups of 12–15 A. andreae workers were hunting. These prey were dropped from ca. 5 cm in height at ca. 2.5 cm from the leaf margins.