Wasp and bee stings are most common; especially on cat paws (from batting them) and puppies’ faces (because they explore everything with their mouths). If you are quick you might be able to remove the bee sting and venom sack before it empties but be careful not to squeeze it!
Wasps don’t leave a sting in, they just inject venom. Ice or cold water soothes the pain and reduces swelling. Ask your vet about a pet-safe antihistamine to keep in your first aid kit. If the sting is around the head or in the mouth, swelling might obstruct breathing. If you are worried consult your vet; occasionally IV steroids are required.
Nettles can sting dogs’ paws leading to intense itching and chewing. Avoid walking through nettles. Again, this would be a time to use an antihistamine recommended by your vet. Some paw waxes might reduce stinging and soothe afterwards.
Adders are present in some parts of the country. They usually slither away before you see them, but at cooler times of day they might be out basking and be too slow to escape. This is when they are most likely to bite (in self-defence). Fatal bites are rare; more often the poison causes pain, swelling, and tissue death. Dogs can develop extensive bruising and ulcerated wounds. Ice or cold water on a bite will reduce the spread of the venom, and pain and swelling. Carry your dog to the car if possible and get emergency veterinary advice. Treatment is usually supportive fluids, pain relief, and antibiotics. Antivenom is hard to get hold of, can cause anaphylactic reactions, and might not improve the outcome in most cases.
At the beach watch out for jellyfish, Portuguese man-o-war, and weaver fish. All cause painful stings. Hot water neutralises the venom but keeping a dog’s foot in very hot water for half an hour could be difficult! Keep your pet calm and visit a local vet for painkilling medication.