Body appendages fine-tune posture and moments in freely manoeuvring fruit flies.

The precise control of body posture by turning moments is key to elevated locomotor performance in flying animals. Although elevated moments for body stabilization are typically produced by wing aerodynamics, animals also steer using drag on body appendages, shifting their centre of body mass, and changing moments of inertia caused by active alterations in body shape. To estimate the instantaneous contribution of each of these components for posture control in an insect, we three-dimensionally reconstructed body posture and movements of body appendages in freely manoeuvring fruit flies (Drosophila melanogaster) by high-speed video and experimentally scored drag coefficients of legs and body trunk at low Reynolds number. The results show that the sum of leg- and abdomen-induced yaw moments dominates wing-induced moments during 17% of total flight time but is, on average, 7.2-times (roll, 3.4-times) smaller during manoeuvring. Our data reject a previous hypothesis on synergistic moment support, indicating that drag on body appendages and mass-shift inhibit rather than support turning moments produced by the wings. Numerical modelling further shows that hind leg extension alters the moments of inertia around the three main body axes of the animal by not more than 6% during manoeuvring, which is significantly less than previously reported for other insects. In sum, yaw, pitch and roll steering by body appendages probably fine-tune turning behaviour and body posture, without providing a significant advantage for posture stability and moment support. Motion control of appendages might thus be part of the insect's trimming reflexes, which reduce imbalances in moment generation caused by unilateral wing damage and abnormal asymmetries of the flight apparatus.

Calcium signalling indicates bilateral power balancing in the Drosophila flight muscle during manoeuvring flight.

Manoeuvring flight in animals requires precise adjustments of mechanical power output produced by the flight musculature. In many insects such as fruit flies, power generation is most likely varied by altering stretch-activated tension, that is set by sarcoplasmic calcium levels. The muscles reside in a thoracic shell that simultaneously drives both wings during wing flapping. Using a genetically expressed muscle calcium indicator, we here demonstrate in vivo the ability of this animal to bilaterally adjust its calcium activation to the mechanical power output required to sustain aerodynamic costs during flight. Motoneuron-specific comparisons of calcium activation during lift modulation and yaw turning behaviour suggest slightly higher calcium activation for dorso-longitudinal than for dorsoventral muscle fibres, which corroborates the elevated need for muscle mechanical power during the wings' downstroke. During turning flight, calcium activation explains only up to 54 per cent of the required changes in mechanical power, suggesting substantial power transmission between both sides of the thoracic shell. The bilateral control of muscle calcium runs counter to the hypothesis that the thorax of flies acts as a single, equally proportional source for mechanical power production for both flapping wings. Collectively, power balancing highlights the precision with which insects adjust their flight motor to changing energetic requirements during aerial steering. This potentially enhances flight efficiency and is thus of interest for the development of technical vehicles that employ bioinspired strategies of power delivery to flapping wings.

Potential targets aimed at by spitting cobras when deterring predators from attacking.

When threatened, spitting cobras eject venom towards the face of an aggressor. To uncover the relevant cues used by cobras for face recognition we determined how often artificial targets equipped with or without eyes elicited spitting behavior. In addition, we measured whether and how target shape and size influenced the spitting behavior of cobras. Results show that oval- and round-shaped targets were most effective, while triangles with the same surface area as oval 'face like' targets hardly elicited spitting. The likelihood of spitting depended on neither the presence, the spatial arrangement (horizontal or vertical) nor the surface texture (shiny or matt) of glass eyes. Most likely, cobras do not specifically aim at the eyes of an offender but at the center of the body part closest to them. As this is usually the face of an animal, this strategy will result in at least one eye of the offender being hit most of the time.

Spitting cobras adjust their venom distribution to target distance.

If threatened by a human, spitting cobras defend themselves by ejecting their venom toward the face of the antagonist. Circulating head movements of the cobra ensure that the venom is distributed over the face. To assure an optimal distribution of the venom, the amplitudes of head movements should decrease with increasing target distance. To find out whether cobras (Naja pallida and N. nigricollis) adjust their spitting behavior according to target distance we induced spitting from different distances and analyzed their spitting patterns. Our results show that the spray pattern of spitting cobras is not fixed. Instead the snake matches its venom distribution to the size of the target independent of target distance.