Does anyone know what bugs these are? These were found on the leaves of our tomato plants.
I don't think these are spider mites, they are aphids, adult and young ones, they just happen to be reddish brown. Aphids can be black, white, red, brown, or green, but the solution is similar. You don't say where you are in the world, but neem oil spray should do the trick, that or insecticidal soap - when spraying, ensure you spray beneath the leaves and the stems, but try to avoid any open flowers if you can. Info here http://homeguides.sfgate.com/tiny-white-things-brown-aphids-tomato-plant-92894.html
These are a type of red spider mites. That’s not good! They are sap sucking insects that reduce the plant vigour and fruit crops, possibly leading to death.
However, I only see adults but no eggs or nymphs yet who will do the most damage. Look for these on leaf underside.
I live in the UK so our control method might be different.
You can use sticky insect trap above your plants to catch adults.
The best control method is biological, using a predatory midge called phytoseiulus persimilis. This works best in greenhouse and is available on the internet, depending where you live.
Obviously, chemicals can be used:
Fatty acid, essential oils can be used: mix 6 drops of each of: rosemary, clove, garlic, peppermint, lavender oil with 1 litre of water and spray. This will dissolve the insect on contact and not affect plants whatsoever. Applications must be frequent for continuous control.
For real chemicals, I can’t advise you unless I know where you live. Also tell me if the plants are inside or outside and how many you have.