Hi and welcome to the forum! :-)
My guess is they run out of energy trying to keep the slime level up. I've asked Botsareus to slow down the decay speed for slime, which may be fixed in the next beta.
So you may want to add a gene so they don't store slime if their energy is too low, like this for example:
' Gene 9 Slime
cond
*.slime 300 <
*.nrg 500 > and
start
100 .mkslime store
stop
If you use costs you need to have genes designed to handle that.
Here are a couple of bots you can try and compare with.
cond
*.eye5 0 >
*.refeye *.myeye !=
start
*.refveldx .dx store
*.refvelup 30 add .up store
stop
cond
*.eye5 50 >
*.refeye *.myeye !=
start
-1 .shoot store
*.refvelup .up store
stop
cond
*.eye5 0 =
*.refeye *.myeye = or
start
314 rnd .aimdx store
stop
cond
*.nrg 16000 >
start
10 .strbody store
stop
cond
*.body 16000 >
start
50 .repro store
stop
' Blind Boticus is a modified version of A. Boticus
'
'Modified by Testlund to use touch senses instead of vision (check Disable Vision).
'
start
.fixpos *.fixed mult dec
51 *51 sgn mult dec
51 *51 sgn -1 mult mult inc
stop
cond
*.nrg 1000 >
start
10 *.vel sub 2 div .up store
stop
cond
*.refup *.myup = or
*.refxpos 0 = and
*51 20 !=
start
314 rnd .aimdx store
51 inc
51 inc
stop
cond
*.refxpos 0 != and
*.refup *.myup !=
start
*.refxpos *.refypos angle .setaim store
8 .fixpos store
-6 .shoot store
stop
cond
*.nrg 5000 >
start
32 .strbody store
stop
cond
*.body 5000 >
start
50 .repro store
stop