From these photos, the main features to go on are the dorsal black and red markings, the coloured bands on the legs, the white dots on the abdomen, and the shape of the body. These features does match well with this species, which is common in southern North America:
Milkweed Assassin Bug
The bite from this species is supposed to be very ...
I think this could possibly be the nymph of some sort of cockroach.
I initially thought these were aphids of some type due to their pear-like body shapes and the small pair of upright projections coming off their backsides (possibly cornicles?).
However, zooming into some of your more-detailed specimens in the 2nd photo ...
My understanding (as a PhD holder in toothed whale echolocation) is that insects do not use echolocation themselves as a means of hunting or sensing their environment more generally, but some do produce clicks which serve to jam/confuse a bat's echolocation. This is an anti-predation strategy. Their production of clicks being a means of defence is supported ...
The size (~2 inches), broad "quadrate" head, and long posterior abdomen leads me to believe this is a relative large larva of a Predaceous Diving Beetle (family Dytiscidae).
The larvae are sometimes called "water tigers" due to their large mandibles and voracity as aquatic predators.
One possible example:
Dytiscus marginalis; Sources:...
The Bloomington Drosophila Stock Center has a lot of information on Drosophila stock propagation. Their Working with Drosophila Stocks guide includes the following excerpt:
The frequency with which new subcultures need to be established depends on the health and fecundity of the genotype, the temperature at which it is raised, and the density of the ...
This appears to be the exuvia (i.e., molted) pupa of some sort of moth.
One Australian species with a similar-looking and sized pupa is the bardee or rain moth (Trictena atripalpis; or Abantiades atripalpis):
Credit: Dianne Clark ; Source: Coffs Harbour Butterfly House
See another similar looking (and coincidentally 8cm long) specimen here: