There are many examples of “suicide” in a range of species, which usually involves sacrifice for the sake of relatives or future relatives. There are a number of spiders in which the females sit with their brood as they hatch and offer their bodies up as a first meal. Some male praying mantises offer their bodies up as nuptial gifts for their lovers to snack on as they mate – they have an extra brain in their thorax (“chest”) that allows them to continue to mate as their heads are eaten. Bees and ants are famous for sacrificing their lives for their colonies – in the case of honey bees they disembowel themselves when they sting intruders in the defence of their queen. This kind of sacrifice is rarer in vertebrates but it still happens in defence of young or other relatives – many ground nesting birds will lure predators away from their nests by acting injured even when they end up being eaten.

There are also examples of individuals being coerced by parasites into sacrificing themselves so the parasite can infect their target predatory host; there’s a microbial parasite of cats that rewires rat brains to make them attracted – even sexually aroused – by cat urine! We also know that human animals kill themselves for a wide variety of reasons. So, yes, animals can definitely kill themselves.