Termite's Twisted Mandible Presents Fast, Powerful, and Precise Strikes

Abstract

The asymmetric mandibles of termites are hypothetically more efficient, rapid, and powerful than the symmetric mandibles of snap-jaw ants or termites. We investigated the velocity, force, precision, and defensive performance of the asymmetric mandibular snaps of a termite species, Pericapritermes nitobei. Ultrahigh-speed recordings of termites revealed a new record in biological movement, with a peak linear velocity of 89.7-132.4 m/s within 8.68 μs after snapping, which caused an impact force of 105.8-156.2 mN. High-speed video recordings of ball-strike experiments on termites were analysed using the principle of energy conservation; the left mandibles precisely hit metal balls at the left-to-front side with a maximum linear velocity of 80.3 ± 15.9 m/s (44.0-107.7 m/s) and an impact force of 94.7 ± 18.8 mN (51.9-127.1 mN). In experimental fights between termites and ant predators, Pe. nitobei killed 90-100% of the generalist ants with a single snap and was less likely to harm specialist ponerine ants. Compared with other forms, the asymmetric snapping mandibles of Pe. nitobei required less elastic energy to achieve high velocity. Moreover, the ability of P. nitobei to strike its target at the front side is advantageous for defence in tunnels.

Figure 1

Snapping mandibles of termite soldiers. (a) In the symmetric snapping of Termes panamaensi^,, elastic energy is stored in both mandibles, as indicated by the deformation and motion of the left (L) and right (R) mandibles. (b) In the asymmetric snapping of Pericapritermes spp., elastic energy is stored in only the left mandible when its anterior part rotates about the joint or pivot point O. The posterior part remains stationary during snapping. (c) Morphology of the twisted left mandible of the Pericapritermes nitobei termite used in this study. The length of the anterior part of the left mandible (L_A) and the mass of its subsections A₁ and A₂ (i.e., M_A1, M_A2) are required to estimate its moment of inertia (I_A). The subsections A₁ and A₂ were prepared by performing two cuts; one cut was made at the pivot point (C₁) and the other was made at the centre of the anterior part (C₂).

Figure 2

Behavioural phases of Pericapritermes nitobei mandibular snaps. (a) Stages 1–3: High-speed recordings from 10 soldiers at 1,000 frames per second (fps) indicated that the right mandible pressed against the left mandible for 261 ± 43 ms before the mandibles slid across each other to snap, and termites raised their antennae 47.5 ± 22.5 ms before the snap (Stages 2–3). Stage 3–4: Single snap of two soldiers (b and c) recorded by an ultrahigh-speed video camera at 460,830 fps. Mandibular snaps were performed over 21.7–43.4 μs. The peak linear velocity (V_MT) of two soldiers at 8.68 μs were 132.4 and 89.7 m/s. Images in (b,c) were obtained by transforming Supplementary Movies S1 and S2, respectively, to frames using codes written in Python language (v. 3.8) with the package opencv-python.

Figure 3

Snap performance of the Pericapritermes nitobei soldier’s asymmetric mandible in ball-strike experiments (92 events from 15 termites, A–O). (a) Motion of the termites and metal ball. When the left mandible hit the metal ball, the termite soldier and ball moved away from each other. Yellow and blue arrows indicate the position of the termite and metal ball, respectively. (b) Linear velocity V_MT. (c) Snapping force F_A. The maximum recorded V_MT and F_A values for each soldier are displayed above each bar. (d) Movement directions of the metal ball. Each blue line indicates a record of one moving metal ball. Angle normality was assessed using the Shapiro–Wilk test. Images in (a) were obtained by transforming Supplementary Movie S3 to frames using codes written in Python language (v. 3.8) with the package opencv-python.

Figure 4

Defensive performance of mandibular snaps by probability (values above each bar) of (a) hitting and (b) killing four predator ant species. Bars with identical letters were not significantly different at p < 0.05 (Fisher’s exact tests with Bonferroni corrections). Termites could not kill their specialist predators Anochetus taiwaniensis and Pachycondyla javanus.

Figure 5

Attack behaviours of (a) Pheidole megacephala, (b) Anoplolepis gracilipes, (c) Anoc. taiwaniensis, and (d) Pa. javanus on Pe. nitobei. The attacks of Ph. megacephala, Anop. gracilipes, and Anoc. taiwaniensis were initiated after their antennae touched the mandibles or head of Pe. nitobei (0 ms), with a short distance between the heads of these three species and the mandible tip of Pe. nitobei (approximately 0.6–1.5 mm). By contrast, Pa. javanus initiated an attack when its head was approximately 6.8 mm away from the mandible tip of Pe. nitobei (0 ms). This attack was followed by rapid movement toward the termite’s head (33.3 ms) and clamping at its mandibles (66.6 ms).