Yes, mole killers can harm other wildlife and beneficial insects. Many mole control products contain toxic chemicals such as bromethalin, zinc phosphide, or anticoagulant rodenticides, which are designed to be lethal to moles. However, these substances do not discriminate between target and non-target species. 
When these poisons are used, they can inadvertently affect other animals that come into contact with them. For instance, birds, small mammals, and even pets may ingest the poison directly or consume poisoned moles, leading to secondary poisoning. This can result in illness or death for these non-target species. 
Additionally, beneficial insects that contribute to soil health and pest control can also be affected. Some mole control methods, like traps, may not directly harm insects, but the use of chemical treatments can disrupt the ecosystem balance. Insects that are crucial for pollination or serve as food for other wildlife may be reduced in number, impacting the broader ecological community.
Moreover, the use of chemical mole killers can lead to contamination of soil and water sources, further affecting a wide range of organisms. This environmental impact can have long-term consequences on biodiversity and ecosystem health.
Therefore, while mole killers can be effective in controlling mole populations, they pose significant risks to other wildlife and beneficial insects. It is important to consider alternative, more environmentally friendly methods of mole control, such as traps or natural deterrents, to minimize harm to non-target species.